This document provides a literature review on healthcare textiles. It discusses the types of textiles used in healthcare like surgical gowns, drapes, and bed linens. These textiles require special properties like antibacterial properties and comfort. A range of natural and man-made fibers with enhanced properties have been developed for healthcare textiles. Blending fibers is often necessary to achieve desired product properties. The document then focuses on the properties and use of lyocell fiber for healthcare textiles.

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CHAPTER 2
LITERATURE REVIEW
2.1 HEALTHCARE TEXTILES
Textile products are used in medical and healthcare sector in
various forms. Healthcare textiles comprise surgical clothing (gowns, caps,
masks, uniforms etc.), surgical covers (drapes, covers etc.) and beddings
(sheets, blankets, pillow cases etc.). The complexity of applications has
increased with research and developments in the area of medical textiles. The
surgical gown, operating room garments and drapes require special anti-
bacterial properties combined with the wearer’s comfort.
A range of natural and manmade fibers with enhanced comfort
properties and anti-microbial properties have been introduced in the market.
These fibers and their blends are being utilized for developing new products
in medical textiles. It is observed that for many products, ideal set of physical
and chemical properties would not be possible to achieve from one fiber
alone. Hence, blending of two or three fibers having differing physical and
chemical properties for the desired product becomes essential. However,
some chemical characteristics of the fiber/fabric are also modified during
fiber manufacture/chemical processing. Sometimes, modified fibers are also
blended to achieve the desired end product.
Use of nanotechnology, tissue engineering, biomaterials along with
basic textile structures, viz, fibers, yarns, woven, knitted, non-woven and
braided fabrics and composite structures made it possible to widen the

2. 9
horizon of medical textiles. Table.2.1 shows the type of fibers used for
different applications. (Rajendran and Anand 2002).
Table 2.1 Healthcare/Hygiene Products and the Fibers Used
Hospital Textile
application
Fabric Fiber Type
Surgical gowns Woven, nonwoven Cotton, polyester, polypropylene
Surgical caps Nonwoven Viscose
Surgical masks Nonwoven Viscose, polyester, glass fiber
Surgical drapes, cloths Woven, nonwoven Polyester, polyethylene
Surgical hosiery Knitted
Cotton, polyester, polyamide
elastomeric- yarns
Blankets Woven, knitted Cotton, polyester
Sheets, pillowcases Woven Cotton
Uniforms Woven Cotton, polyester
Protective clothing,
incontinence, diaper/sheet,
coverstock
Nonwoven Polyester, polypropylene
Absorbent layer Nonwoven
Superabsorbent fibers, wood
fluff,
Outer layer Nonwoven Polyethylene fiber,
Cloths/wipes Nonwoven Viscose, lyocell
Most of the hospital textiles are made of polyester cotton and their
blends. Viscose fiber is used in the form of nonwovens for few selected
applications.
2.2 QUALITY REQUIREMENTS OF BED LINEN
Bed linen is a sheet of material used to cover the bed, which should
be soft with warm handle and easy care properties. The majority of the bed
linen is made from cotton and polyester/cotton blended yarns. Depending on
the end use, cost factor, durability of the textiles, comfort and aesthetic

3. 10
properties, the fiber choice is made from natural fiber, regenerated cellulosic
fibers and synthetic fibers.
2.3 CHARACTERISTICS OF FIBERS USED FOR
PRODUCTION OF HOSPITAL TEXTILES
In this research work, different varieties of fibers and their blends
are used for producing hospital textiles and each fiber has its own special
characteristics which are discussed below.
2.3.1 Properties of Lyocell Fiber
Lyocell is a regenerated cellulosic fiber manufactured by a closed
loop process, involving dissolution of wood pulp in N- methyl- morpholine-
N- oxide. The manufacturing process of lyocell is different from that of other
regenerated cellulosics such as viscose rayon, in that it proceeds without the
formation of intermediate compounds and there is no curing or ripening stage.
The manufacturing process imparts to lyocell a unique combination of
properties compared to other regenerated cellulosics, such as high wet
strength, high wet modulus, high crystalline and amorphous orientation, high
crystallinity and high wet swelling, which influence its behavior in wet
treatments.
Like other cellulosic fibers, lyocell is breathable, absorbent and
comfortable to wear in conditions of high humidity because it is cellulosic
which causes moisture to be wicked away from the skin.
2.3.1.1 Moisture transport properties of Lyocell fiber
In contrast to synthetic fibers with reduced wicking properties,
lyocell offers unique moisture transport ability. This property of lyocell
guarantees optimum conditions for the skin. The figure 2.1 shows distribution

4. 11
of moisture in the cross section of cotton, lyocell and polyester fiber (Heinrich
Firgo et al 2006).
Cotton lyocell polyester
Figure 2.1 Cross Section of Cotton, Lyocell and Polyester Fibers
The illustration shows that in contrast to cotton and polyester fibers,
lyocell controls and regularly absorbs moisture. It absorbs 50 % more
moisture than cotton. Compared to the other two fibers, lyocell features the
highest moisture absorption rate: with air humidity at 65 %, lyocell still has
unused capacity to absorb moisture from the skin. Figure 2.2 compares the
surface structure of lyocell and cotton fibers (Schurz 1994)
Lyocell Cotton
Figure 2.2 Surface Structures of Lyocell and Cotton Fibers.
Lyocell fiber has an extremely smooth surface and feels soft and
pleasant on the skin. The combination of a smooth fiber surface and excellent
moisture absorption creates a positive environment for healthy skin, making
lyocell ideal even for anyone with sensitive skin. According to recent
dermatological studies, wearing clothing made of lyocell significantly
improves comfort and promotes a feeling of well being (Thomas et al 2006).
Also, lyocell is chemical-free, ecofriendly fiber, an important factor for
sensitive skin in comparison to other fibers of natural origin.

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Lyocell is often blended with other natural fibers such as wool,
cotton, silk, flax and various manufactured fibers. When blended with other
fibers, it gives a wonderful sheen to the yarn and adds softness to many other
fibers. Cotton blended with lyocell becomes stronger and wool/lyocell blends
are more absorbent. The properties of lyocell fiber with different deniers are
given in the Table 2.1.
Table 2.1 Properties of Lyocell Fiber
Unit Fiber DenierFiber property
Dtex 0.9 1.3 2.2 1.4 3.0
Cut length mm 34 38 50 38 75
Tenacity cN/tex 36 34 33 36 31
Elongation % 12 10 10 10 10
Tenacity (wet) cN/tex 30 28 26 25 19
Elongation(wet) % 13 12 12 10 10
MoistureRegain % 11 11 11 8 9
2.3.1.2 The structural model of Lyocell fiber
A lyocell fiber consists of countless hydrophilic, crystalline nano-
fibrils which are arranged in a very regular manner. Water absorption occurs
only in the amorphous domains and capillaries between the crystalline fibrils.
A lyocell fiber therefore is a unique hydrophilic nano-structure which is the
reason for the special water management, comfort and other positive features
of lyocell. Abu-Rous (2006) made an effort to explain the functional and
wellness properties in lyocell textile using the nano structure of lyocell. The
special functional and wellness properties of lyocell textiles is due to the
cool and smooth surface (gentle to the skin) and the wear comfort properties
due to excellent moisture transport, buffering and the temperature control.
The background for this property is the unique structure of lyocell fibers

6. 13
which contains a compact core, a porous middle zone and a semi-permeable
fiber skin. Applying fluorescence microscopy and TEM on fiber cross-
sections, different porous zones could be discriminated, partly confirming the
model mentioned above. Figure 2.3 shows the structural model of lyocell
fibers (Christian Schuster 2006).
Figure 2.3 Structural Models of Lyocell Fibers
Presence of superfine or micro fibrils provide greater specific
surface area, greater vapour transmission, lower flexing resistance, softer
handle, greater crease resistance and greater fabric density and cover to the
lyocell fiber. These advantages provide the yarn with more pores to transport
vapour out by their superior capillary action. The higher pore density also
provides better thermo regulation.
In general, the lyocell fibers show higher porosity than natural
fibers, leading to outstanding water buffering capacity. In lyocell, the water
accessible pores are distributed very evenly in the fiber cross-section. The
cool touch of lyocell can be explained by the quick removal of water vapour
from the fiber when the textile is touched and heated up by skin contact. The
very accessible interconnected pore network seems to play a major role in the
fast conduction of moisture in the fiber (wicking effect). Additional effects of

7. 14
the high water uptake in lyocell are minimized bacterial growth and less
odour formation.
Heinrich Firgo et al (2006) analyzed the comfort properties of
single layered and double layered fabrics made of tencel/ polyester blended
yarns in the face of the fabric and polyester as the skin contact layer. From
the experimental results the authors concluded that tencel can be used
effectively for the development of high performance sportswear provided that
the fabric is carefully designed to maximize the contribution of the tencel to
the performance of the fabric.
Friedrich et al (2002) presented a comparative analysis of thermal
insulation properties of fabrics made of cotton and tencel with different weave
structures. The fabrics made of tencel yarn showed lower values of thermal
conductivity and thermal absorption and also higher values of thermal
diffusion and resistance than fabrics made of cotton yarns. Twill woven
fabrics made of lyocell have higher air permeability and thermal resistance
compared to plain woven fabrics.
Thomas et al (2006) evaluated the skin compatibility of
commercially available tencel textiles in patients suffering from atopic
dermatitis or psoriasis in an everyday situation. The patients gave excellent
scores for tencel textiles regarding improvement of itching, skin sensitivity,
thermoregulatory properties, for its properties of cool, smooth and dry feeling,
and for its compatibility with the local topical treatment. Hence tencel textiles
significantly contribute to well-being also under dermatological conditions.
From a dermatological point of view these textiles can be recommended not
only for healthy subjects but also for people with sensitive skin or even
patients with skin disease, especially atopic dermatitis or psoriasis
(Heidelberg 2004). Avinash (2005) studied about the drying rates of resin
treated lyocell fabrics. Cheunsoon (2005) evaluated the physical and fabric

8. 15
hand characteristics of lyocell fabrics made with different wood pulps and
stated that, the production of lyocell fibers and physicochemical traits play
interrelated roles in making lyocell with desired properties.
2.3.2 Properties of Micro fibers of Lyocell and Polyester
Synthetic fibers having fineness below 1.0 denier are called as
microfibers. Micro fibers have distinguishing properties such as softness, full
handle with excellent drapeability and comfort (Basu 2001).
Superfine or microfiber yarn enables very dense fabrics to be
produced with extended specific fabric or fiber surface area, developing more
pores to transport vapour out by their superior capillary action. The higher
pore density also provides better thermo regulation. Finer fibrils will provide
higher specific area, better vapour transmission, softer handle, higher fabric
density, better cover and lower flexing resistance (Prabhakar Bhat and
Bhonde 2006). Comfort properties of polyester microfiber fabric are more in
terms of wicking when compared with micro polyester /cotton blends and
pure polyester non- micro fiber fabrics. (Ramachandran et al 2009). Schacher
et al (2000) compared the thermal insulation and thermal properties of
classical and microfiber polyester fabrics.
Rose and Matic-Leigh et al (1993) carried out a study on the
aesthetic and comfort properties of microfiber blended knitted fabrics to
determine the effect of micro-fiber staple yarns on knit fabric performance.
Sandip et al (2007) reviewed about micro fibers, their classification,
manufacturing methods, different fiber forms, general properties and their
applications. Sampath et al (2009) studied the effect of stitch length and knit
structure on the wicking, wetting, water absorbency, moisture vapour
transmission and air permeability of moisture management finished micro
denier polyester knitted fabrics.

9. 16
2.3.3 Properties of Bamboo Fiber
Bamboo fiber is a natural, green and eco friendly textile material of
the 21st century, which is made of 100% bamboo pulp. In textile form,
bamboo retains many of the properties it has as a plant. Bamboo is highly
water absorbent, able to take up three times its weight of water.
Bamboo fiber is characterized by its good hygroscopicity, excellent
permeability, soft feel, easiness to straighten and dye, and splendid color
effect of pigmentation. It is also a new environment-friendly fiber which is
both anti-bacterial and deodorizing in nature. Bamboo fabric has an unusual
level of breathability, making it incredibly cool and comfortable to wear. This
is because the cross-section of the bamboo fiber is filled with various micro-
gaps and micro-holes; it has much better moisture absorption and ventilation
(Parameswaran and Liese 1976). This character of the fiber translates to an
excellent wicking ability that will pull moisture away from the skin so that it
can evapourate. For this reason, clothing made of bamboo fiber is often worn
next to the skin. With this unique microstructure, bamboo fiber apparel can
absorb and evapourate human sweat very quickly. In addition, bamboo fabric
has insulating properties and will keep the wearer cooler in summer and
warmer in winter. (Nazan Erdumlu and Bulent Ozipek 2008). Bamboo owns a
unique anti-bacteria and bacteriostatic bio-agent named "bamboo kun" which
gives the inherent antimicrobial property to the bamboo fiber.
The physical properties of bamboo fiber are given in Table 2.3
(China Textile Industry Testing Institute 2004)

10. 17
Table 2.3 Physical Properties of Bamboo Fiber
S.No Parameter Value
1. Dry tenacity (cN/tex) 23.3
2. Wet tenacity(cN/tex) 13.7
3. Dry elongation at break (%) 23.8
4. Whiteness 69.6
5. Moisture regain (%) 13.03
Bamboo fiber has excellent moisture regain and elongation but the
wet and dry tensile strength are comparatively less than cotton fiber. Abhijit
Majumdar et al (2010) presented the thermal properties of different knitted
fabric structures made from cotton, regenerated bamboo and cotton-bamboo
blended yarns and found that the thermal conductivity of knitted fabrics
generally reduces as the proportion of bamboo fiber increases. The interlock
fabrics have higher thermal conductivity and thermal resistance values and
lower water vapour permeability and air permeability when compared to plain
fabrics.
2.3.4 Properties of Bamboo Charcoal Fiber
Bamboo charcoal, is a non graphite form of activated carbon made
from pieces of bamboo plants which are five years or older, by carbonizing
inside an oven at temperatures over 800°C and then converted into powder
form. Fibers from bamboo charcoal can be produced in many kinds, such as
single and multi-filament; staple fiber and it can also be spun with pure
cashmere, cotton and other fibres. There are two main ways to produce
bamboo charcoal fiber: the first way is to add nano-bamboo charcoal powder
during the process of spinning in the spinning solution; the second is to add
the established bamboo charcoal composite polymer master-batch in the stage

11. 18
of synthesizing fiber. Bamboo charcoal viscose fiber can be produced from
natural plant cellulose pulp by adding bamboo charcoal micro powder milk
dissolved by the solvent and then spinning the solution by extrusion and
solidification. Polyester based bamboo charcoal fiber is produced in the
similar way from polyester master batch with bamboo charcoal content about
50%. Similarly bamboo charcoal nylon fibers and bamboo charcoal magnetic
fiber series are also produced (Jeong-Sook Cho and Gilsoo Cho 1997; China
Textile Team 2009).
Since the Bamboo charcoal fiber contains activated carbon, which
is efficient in adsorbing odorous volatile micro-organism, thereby reducing
the odor and growth of micro-organisms, it is used in hospital textiles for
reduction of microbial growth and adsorption of wound odor (Robert Czajka
2005). The unique properties of bamboo charcoal include uniform
composition, high porosity, anti-bacterial and anti-fungal property,
breathability, thermal regulation, odor control, absorption and emission of Far
Infrared energy, preventing static electricity buildup and good wash durability
(Chin-An Lin and Ta-Chung An 2007). These fabrics can absorb and disperse
sweat fast, making them feel dry and comfortable. They also do not stick to
skin on hot summer days. Bamboo charcoal fabrics absorb and decompose
benzene, phenol, methyl alcohol, and other harmful substances. As the
bamboo-charcoal nano particles are embedded in the fiber rather than simply
coated on the surface, these fabrics are washable without diminished
effectiveness of the charcoal powder's special qualities, even after 50 washes
(Parthiban and Viju 2009). Thenmozhi et al (2010) analyzed cotton, bamboo
/ cotton and bamboo charcoal bed linens for their suitability as hospital
textiles by applying anti-microbial and blood repellant finish and it was found
that anti-microbial activity, blood repellency and odor resistance is higher for
bamboo charcoal fabrics than 100% bamboo /cotton union fabrics or 100%
cotton fabrics.

12. 19
Jeong-Sook Cho and Gilsoo Cho (1997) have recorded that, as the
activated carbon is efficient in adsorbing odorous volatile micro-organism
thereby reducing the odor and growth of micro-organisms, it is used in
hospital textiles for reduction of microbial growth and adsorption of wound
odor.
Kuruvilla et al (2008) made an attempt to study the usefulness of
Activated Carbon Fabric mask (ACF) to prevent lead absorption. Indigenous
ACF masks were provided to eight workers involved in the manufacture of
batteries and their blood lead levels were determined before and after using
these masks. There was a substantial decrease in blood lead level after using
the mask among those who were under treatment for high blood lead levels.
Han Chien Lin et al (2008), examined on the usage of the original
bamboo vinegar collected from Moso bamboo (Phyllostachys heterocycla) at
six different temperatures to increase the fungi resistance of bamboo.
Splendore et al (2010) evaluated the thermo-physiological comfort of a
knitted polyester (PES) fabric which contains activated carbon particles in the
back-side. The activated carbon particles, added in the PES extrusion process,
give permanent attributes to the garment, such as odour resistance, UV
protection and evapourative cooling which makes the modified PES ideal for
sportswear.
2.4 PROPERTIES OF BLENDED YARNS AND THEIR
APPLICATIONS
It is apparent that the type of raw material and fabric structure
influence the properties of finished goods. Blending of different fibers is done
to enhance the performance and improve the aesthetic qualities of fabrics and
are selected and blended in certain proportions so that the fabric will retain
the best characteristics of each fiber. Fiber selection is done based on the

13. 20
properties like moisture management, thermal conductivity, breathability,
wettability, wickability, natural stretch and dimensional stability.
Blending of different types of fibers and analysis of the comfort
characteristics of blended fabrics have been carried out by various researchers
in the past. Kothari (2006) has discussed the role of fiber properties on
comfort characteristics of fabric and studied how the blending of fibers at
yarn manufacturing stage can lead to fabrics having the desired characteristics
from comfort point of view. The results of experimental study of water
vapour permeability of polyester/viscose and polyester/cotton blended fabrics
showed that higher the polyester content in P/V and P/C fabrics, lower is the
water transmission ability. Air permeability increases with increase in
polyester content and the water vapour transmission rate also increased with
the air flow rate of the above fabric.
Yoon and Buckley (1984) determined the mechanical and surface
properties for polyester, cotton and polyester/ cotton blended knit fabrics. The
polyester fabric showed a higher resistance to tensile deformation than the
cotton fabric, while the blend fabrics showed an intermediate resistance in
accordance with the blend level.
Yoon and Buckley (1984) determined the thermal transport
properties of a series of polyester, cotton and polyester/cotton blended fabric
in an effort to understand the physical basis of clothing comfort. The results
indicated that both the fabric construction and the constituent fiber properties
affect thermal comfort. In general, thermal insulation, air permeability and
water vapour transmission rate are dependent mainly on the fabric
geometrical parameters namely thickness and porosity. Conversely, liquid
water transport is strongly dependent on the constituent fibers with cotton
generally showing advantages over polyester.

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Brojeswari Das et al (2009) studied the moisture related properties
of plain woven polyester/viscose blended fabrics with different polyester
proportion, yarn count and twist, using a three variable factorial design
proposed by Box and Behnken and concluded that proportion of polyester in
the blended fabric affects the comfort characteristics of the fabric.
Nayak et al (2009) probed the effect of polyester content, pick
density and weave on the thermal comfort and tactile properties of polyester/
viscose blended yarn fabrics for suiting, by measuring the low stress
mechanical properties on Kawabata evaluation system and reported that
increasing polyester content increased fabric hand but decreased fabric
smoothness, softness, fullness and total hand value and increased thermal
insulation and water vapour resistance.
Behera (2007) studied the handle and comfort properties of fabrics
made of 100% linen and their blends with cotton and viscose, and reported
that total hand value (THV) of linen fabric is higher than that of cotton fabric
and blending of viscose and cotton improves the hand value of linen fabric
Tyagi (2009) sorted out the thermal comfort behavior of fabrics
made of polyester /viscose and polyester/cotton ring and MJS yarns and states
that the hydrophilic groups of man-made cellulosic component of the fiber
mix governs the liquid moisture transport through capillary interstices in
yarns and concludes that polyester/ viscose fabrics are more promising than
polyester cotton fabrics for comfort applications.
Mukhopadhyay et al (2002) used KES to determine the effects of
blend proportion on the comfort properties of polyester / viscose blended
plain and twill suiting fabrics. Increasing polyester content decreased the total
hand value and increased thermal insulation and water vapour resistance.
Sharabaty et al (2008) have explained about moisture transport through

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polyester/cotton fabrics stating that the hospital bed sheets are commonly
produced from the mixture of cotton and PET fibers. These sheets become
uncomfortable in humid days when cotton fibers become saturated with
moisture, producing uncomfortable sensation which may cause frictional
festers on patient’s skin.
For effective moisture transports properties, several multi layered
fabrics were produced, considering the following aspects:
Hydrophobic layer: This layer must have the capability to
transfer the moisture out of contact surface while maintaining
its hydrophobicity and at the same time, to keep a dry contact
surface between patient body and the bed sheet. But the
migration of moisture stops when the other side is wet. So, to
increase the moisture transfer, its chemical potential has to be
decreased, e.g. making the external layer out of cotton.
Hydrophilic layer: This layer allows obtaining an effective
moisture management of human sweat.
Yingchun Du and Jin Li (2010), investigated the dynamic moisture
absorption behavior of polyester/cotton fabrics of different warp and weft
densities, and the results showed that the fabric moisture absorption velocity
is in reverse relation with its warp and weft densities. They also developed a
mathematical model for the fabric’s dynamic moisture absorption which is
represented in the form of a non-linear partial differential equation. Gene
Cone (2009) has analyzed on the advantages of using blended fabrics in
achieving the required comfort properties and thermoregulation of the human
body by radiation, conduction and sweating.

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2.5 ANALYSIS ON THE PHYSIOLOGY OF HUMAN BODY
AND COMFORT
The human body continuously generates heat by its metabolic
processes. The heat is lost from the surface of the body by convection,
radiation, evapouration and perspiration. In a steady-state situation, the heat
produced by the body is balanced by the heat lost to the environment by
maintaining the body core temperature around a small range, between 36°C
and 38°C. The skin is the major organ that controls the heat and moisture
flow to and fro the surrounding environment. Gilat (1963) and Brojeswari Das
(2007) elaborated on the processes involved in human comfort such as
physical, thermo-physiological, neuro-physiological and psychological states
of comfort.
A base level of metabolism has been defined as the metabolism of a
seated person resting quietly and for a man of typical height and surface area,
the metabolic rate is about 100W. To normalize among people of different
sizes, metabolism is typically expressed in per unit skin surface area. A
specialized unit, the ‘met’ has been defined in terms of multiples of basal
metabolism: one met is equal to 58.15 w/m². A sleeping person has the rate of
0.7 met, and reclining awake is 0.8met. Office work (a mostly seated activity
but one that involves occasionally moving about) is 1.2 met: Walking slowly
(0.9 m/s or 2 mph) is 2 met, moderate walking (1.2 m/s or 2.7 mph) is 2.6
met, and fast walking is 3.8 met and jogging 8 to 12 met. In terms of energy, a
sleeping person has the rate of 40.71 w/m², and reclining awake is
46.52 w/m², Office work is 69.78 w/m² (Federico Butera 1998).
2.5.1 Mechanism of Thermal Regulation of Human Body
The body’s heat losses are through radiation, convection,
conduction, evapouration and through respiration. In a neutral environment,

17. 24
where the body has no need to take thermo regulatory action to preserve its
balance, evapouration provides about 12% of total heat loss and sensible heat
loss provides 88%. In general, the heat transfer by conduction through the
soles of the feet or to a chair is small, around 3%. In normal indoor
environments with still air, the convective and radiation heat transfer are
about equal. In the outdoors, wind strongly affects convective heat loss or
gain and radiation can also cause large losses and gains.
Sweating is important for heat regulation, and it is also a major
source of water absolute loss. There are two types of water loss: insensible
perspiration and sweating. Insensible perspiration loss from the skin cannot be
eliminated. Daily loss is about 400 ml in an adult and the respective heat loss
is 238 kcal. The heat loss can be quite significant because there is a loss of
0.58 kcal for every ml of water evapourated. The maximum rate of sweating
is up to 5 ml/min or 2000 ml/hr in an acclimatized adult. This rate cannot be
sustained, but losses up to 25% of total body water is possible under severe
stress and could be fatal.
There is always a constant amount of trans-epidermal loss of water
vapour directly diffused through the skin resulting in heat loss by insensible
evapouration. In addition the breathing cycle involves humidifying exhaled
air producing another evapourative heat loss. The transversal moisture
diffusion is about 100 to 150 ml per day per m² of skin surface representing a
heat loss of 6% as great as the evapouration from a fully wetted surface. The
respiratory portion of the body’s total heat loss is estimated to be 12%
depending on the metabolic rate.
Clothing is used outside the skin to extend the body’s range of
thermoregulatory control and reduce the metabolic heat by thermo regulation.
It reduces sensible heat transfer, while in most cases, it permits evapourated
moisture to escape. Bed clothes are a form of clothing used for sleeping,

18. 25
because the metabolic rate during sleep is lower than the basal rate and the
body‘s skin temperature tends to be higher during sleep, bed clothes typically
have a higher insulation value than clothing.
2.5.2 Measurement of Conductive, Convective, Radiative and
Evaporative Heat transfer through Fabrics
In order to clarify the heat transfer area involved in convective heat
exchange for the human body, which is required for calculating heat exchange
between the human body and the environment, Yoshihito Kurazumia et al
(2004) calculated the total body surface area of six healthy subjects and the
non convective heat transfer area and floor and chair contact areas for the
various body positions. The effective thermal convection area factor for nine
common body positions such as standing, sitting in a chair, sitting in the seiza
position, sitting cross-legged, sitting sideways, sitting with both knees erect,
sitting with a leg out, and the lateral and supine positions are measured. The
results showed that the effective thermal convection area factor for the naked
whole body in the standing position was 0.942, when sitting in a chair 0.860,
when sitting in a chair, excluding the chair contact area 0.918, in the seiza
sitting position 0.818, in the cross-legged sitting position 0.843, in the
sideways sitting position 0.855, in the both-knees-erect sitting position 0.887,
in the leg-out sitting position 0.906, in the lateral position 0.877 and the
supine position 0.844. For all body positions, the effective thermal convection
area factor was greater than the effective thermal radiation area factor, but
smaller than the total body surface area.
Yoshihito Kurazumia et al (2008) scrutinized the convective and
radiative heat transfer coefficients of the human body, while focusing on the
convective heat transfer area of the human body. Thermal sensors, directly
measuring the total heat flux and radiative heat flux, were employed. The
mannequin was placed in seven postures.The regression equations for the

19. 26
convective heat transfer coefficients (hc [W/ (m2
K)]) for natural convection,
driven by the difference between the mean skin temperatures corrected using
the convective heat transfer area and the air temperature, are given below:
Standing (exposed to atmosphere) hc = 1.007 T 0:406
Standing (floor contact) hc = 1.183 T0:347
Chair Sitting (exposed to atmosphere) hc = 1.175 T0:351
Chair Sitting (contact with seat, chair
back and floor) hc = 1.222 T 0:299
Cross-Legged Sitting (floor contact) hc = 1.271 T 0:355
Legs-out Sitting (floor contact) hc =1.002 T 0:409
Supine (floor contact) hc = 0:881 T 0:368
where hc is the convective heat transfer coefficient [W/(m2
K)], and
T the difference between mean skin temperature corrected using convective
heat transfer area and air temperature [K].
Richard et al (1997) analyzed the convective and radiative heat
transfer coefficients for individual human body segments and found that the
radiative heat transfer coefficient measured for the whole-body was
4.5 W/(m2
K) for both the seated and standing cases, closely matching the
generally accepted whole-body value of 4.7 W/(m2
K). Similarly, the whole-
body natural convection coefficient for the manikin fell within the mid-range
of previously published values at 3.4 and 3.3 W/(m2
K) when standing and
seated respectively. In the forced convective regime, heat transfer coefficients
were higher for hands, feet and peripheral limbs compared to the central torso
region. The ASHRAE Handbook of Fundamentals (1993) has indicated a
linearized radiative heat transfer coefficient hr=4.7 W/m2
per K which has
been widely accepted as a reasonable whole-body estimate for general

20. 27
purposes (Fanger 1977). Byron W Jones (1998) addressed the need to include
the radiation non-uniformity commonly found in indoor environments in body
heat loss calculations.
Extensive research has been carried out to evaluate the sweating
rate. In 1998, Toshio Ohhashi et al. reviewed the methods of human
perspiration evaluation. In 1986, Kraning and his co-operator reported a new
forced-evapouration-type skin capsule for measuring local sweat gland
activity in humans. Shamsuddiny and Togawa (1998) reported a method of
continuous monitoring of sweating in which deion solution was perfused at a
constant flow rate through a chamber attached to the skin surface.
2.6 CAUSES FOR DISCOMFORT AND SKIN DAMAGE IN
MATTRESSES
One of the common manifestations of chronic disease and disability
is the abnormal loading of skin and other surface tissues unaccustomed to
bearing large mechanical forces. A result of abnormal mechanical loading of
surface tissues is breakdown. Though breakdown might appear initially as
only a slight reddening of the skin, it can develop into a significant injury that
damages tissues through the entire thickness of the body wall. If loading
continues unchanged in an area that demonstrates early breakdown,
irreversible injury and necrosis might occur. More extensive pressure ulcers
develop which extend deeper into subcutaneous tissues, sometimes into joint
or body cavities.
There is also compelling evidence that factors in addition to
pressure are contributors and must also be considered when attempting to
fully understand the pressure-sore phenomenon. Studies have implicated
factors such as shear stress (Bennett et al 1979), impact loading of tissue
(Brand 1976), elevated temperature and humidity (Hyman and Artigue 1976)

21. 28
age, nutritional status, general health, activity level (Fisher and Patterson
1983), deformity, posture and postural change, (Hobson DA 1984; Zacharkow
1984) body stature, (Garber and Krouskop 1982) and psychological deficits.
Increased friction and shear, poor nutrition, disease, and pressure aggravate
compromised skin. Even the chemical irritation of frequent washings with
soaps can cause irritation. The adhesiveness of moist skin to bed linens is
estimated to increase the risk of ulceration fivefold. Other causes include poor
nutrition, age, very thin (emaciated), over weight (obese), and suppressed
immune system, radiation therapy, chronic diseases, incontinent, trauma,
swelling & infection.
The roll of few causative factors in pressure ulcer development
(Krouskop 1993) is listed below.
Pressure: Bedsores form where the weight of the person's body
presses the skin against the firm surface of the bed. The pressure that causes
bedsores does not have to be very intense. Pressure of less than 25% the
pressure of a normal mattress can lead to bedsores. Complete muscle necrosis
was demonstrated at 100 mmHg for 6 hours and pressures of 70 mm Hg for
2 hours resulted in pathologic changes within muscle and that lower pressures
of 35 mmHg for 4 hours resulted in no changes(Joan et al 1995).
Temperature: The metabolic heat generated by the body must be
transferred through the bed linen and failure of which leads to increase in
interface temperature between the body and mattress. Elevated body
temperature raises the metabolic activity of tissues by 10% for every one
degree Celsius of temperature increase, concurrently increasing the need for
oxygen and an energy source at the cellulose level. If the patient has impaired
circulation from local pressure and shear, tissues will starve and release
lysozymes, inducing autodigestion of cytoplasma and reducing skin integrity.

22. 29
It has been shown in animal studies that pressure induced tissue injury
accelerates with increasing body temperature (Mahanty and roumer 1980).
Shearing and friction: shearing and friction causes skin to stretch
and blood vessels to kink, which can impair blood circulation in the skin. In a
person confined to bed, shearing and friction can occur when the person is
dragged or slid across the bed sheets. Shear stress occurs when a force is
applied in the plane of the skin surface. Friction occurs when there is
displacement between the skin and the supporting surface.
Moisture: Wetness from perspiration, urine or feces can make the
skin too soft and more likely to be injured by pressure. Moisture from
sweating or incontinence will hydrate the skin, dissolve the molecular
collagen cross links of the dermis, and soften the stratum corneum. Another
result of skin hydration is the rapid increase of the epidermal friction
coefficient, which promotes adhesion of the skin to the support surface and
increase shear, easy sloughing, and ulceration.
2.6.1 Scope and Cost of Skin Breakdown
Research studies show a prevalence of decubitus ulcers in
11 percent of the hospitalized population and in 20 percent of nursing home
residents at any given time (Sanders 1992), For patients in nursing homes, the
prevalence of pressure sores (of Grade 2 or greater) ranges from 7 to
35 percent (Allman et al 1986), resulting in a four-fold increase in mortality
(Norton et al 1975). In Spinal Chord Injured patients, pressure ulcer incidence
is as high as 42 to 85 percent in some centers (Richards 1981). Amputees
using prosthetic limbs are also at risk of breakdown, as a result of the
mechanical forces at the residual limb-socket interface. Over 43,000 new
major amputations are performed per year in the US (Kay and Newman
1975), with 58 percent of them on patients between the ages of 21 and 65

23. 30
years (trauma, cancer, congenital). Thus, there is a significant patient
population of young people with amputation, a group likely to conduct
strenuous activities when using their prosthetic limbs. For those persons with
amputation over 50 years old, vascular causes are the etiology in 89 percent of
the cases (Sanders 1986). Their skin is typically at high risk of breakdown.
2.6.2 Measures of preventing Skin Damage
The principal approach in the past to the challenge of maintaining
healthy skin and avoiding breakdown has been prevention. For example,
patients restricted to bed rest, a subject population at high risk of pressure
ulcer formation, will be turned frequently by the nursing staff to relieve
prolonged pressure. Mattresses designed to cyclically change the distribution
of pressure have been developed. Thus, current prevention programs are
designed to reduce force levels and loading durations below those that cause
breakdown.
Prevention measures also involve the application of interface
surfaces (mattresses, cushions, liners) and frequent pressure reliefs to avoid
sustained pressures in one position. It is interesting to note that skin and body
wall tolerance for sustained pressures typically increases over time (Yarkony
1993).
Skin adaptation and breakdown prevention do exist (Griffiths 1963;
Herceg and Harding 1976; Daniel and Faibisoff 1982). A mobilization
program for an individual with spinal chord injury who has undergone
myocutaneous flap surgery for a pressure sore is an excellent example. (Joan
et al 1995) McInnes (2008) reviewed on Pressure ulcers and the preventive
measures carried out in both institutional and non-institutional settings.
Christine (2004) reviews suggested guidelines for the prevention and
management of pressure ulcers. Prentice et al (2003) published two papers on

24. 31
An Australian model for conducting pressure ulcer prevalence surveys, and
Pressure ulcers: the case for improving prevention and management in
Australian health care settings and analyzed the prevalence of pressure ulcers
in Australia and their causes.
2.6.3 Skin Ulcers formation in Wheel Chair Users
Ulcers in the buttocks area are prevalent among wheelchair users
who have limited mobility, decreased sensation or both. Additionally, many
wheelchair users tend to sit on their cushions for extended periods of time.
Historically, high pressures at the buttocks to cushion interface and extended
sitting times have been identified as the principle contributing factors in
causing skin ulcers. (Vert Mooney et al 1971) As a result, cushion designs
have been focused on decreasing overall and peak pressures during sitting.
New data shows that skin temperature and relative humidity at the
buttocks/cushion interface may be as important as pressure in preventing the
formation of skin ulcers. (Laizzo 2004). Higher temperatures produced both
cutaneous and deep tissue damage.
The study carried out by Vert Mooney et al (1971) for comparison
of pressure distribution qualities in seat cushions confirms that presently
available cushions failed to demonstrate that any of the cushions tested were
safe for prolonged sitting by paralyzed patients. Guldemet Basal and Sevcan
Ilgaz (2009) developed a functional fabric for pressure ulcer prevention. For
this purpose, face-to-face velour weaving technique was utilized to produce a
spacer fabric from the different combinations of engineered polyester,
polypropylene, cotton and viscose fibers. Channeled polyester, cotton and
polypropylene were determined as the most promising fiber types for the final
product.

25. 32
Xiaohua Ye et al (2008), developed a warp knitted spacer fabrics
for cushion application using PES multi filaments for surface layers and PES
mono filaments as the spacer yarn. The results showed that the warp knitted
spacer fabrics have better pressure relief properties, higher air permeability,
and lower heat resistance than PU foam, and thus could be used to substitute
PU foam, especially in the case where the comfort and recycle are highly
required.
2.7 PRESSURE RELIEVING MATTRESS OR SUPPORT
SURFACES
Many types of pressure relieving support surfaces are available
such as water beds, Sheepskins and Australian Medical sheepskin made of
high quality wool etc. An attempt to reduce pressure on a bony prominence is
based on two concepts. Either area in contact with the support surface can be
increased, or contact can be temporarily removed or shifted to other areas. In
the first case immersion and envelopment are the phenomena that produce
reduction in pressure at bony prominence. In the second, the change in areas
of contact over time is the therapeutic consideration. To be effective, support
surfaces must mould to the body to maximize contact, and then redistribute
the patient’s weight as uniformly as possible. They are designed to work on
the principle of Pascal’s law, which states that the weight of the body floating
on a fluid system is evenly distributed over the entire surface as pressure is
increasingly distributed over more body surface area the intensity of pressure
decreases over all body areas. Support surfaces also use the principle of the
deformation, meaning they must be capable of deforming enough to permit
prominent areas of the body to sink in to the support. The surfaces also must
be able to transmit pressure forces from one body area to another. (Maklebust
et al 1986; Elizabeth McInnes 2008; David et al 2000).

26. 33
The degree of head elevation can affect the clinical effectiveness of
a support surface. When the head of the bed is elevated, pressure is shifted to
the sacral and ischial areas of the body. The patient may bottom out if the
seating area of the support surface flattens and looses volume. If the
bottoming out occurs, the support surface no longer provides therapeutic
benefit.
2.7.1 Types of Support Surfaces
The centre for Medicare services divides the support surfaces into
the following three groups
Group I: These surfaces do not require electricity and include air,
foam, gel and water mattresses and overlays (Damien J Jolley et al 2004).
These surfaces are intended for pressure ulcer prevention. Foam surfaces
come in various densities, depth and construction. To reduce pressure, foam
must be of high quality and at least four inches (10 cm) thick. Static air
overlays have multiple chambers that allow air exchange between
compartments when a person lies on the surface. The air exchange between
cells allows the surface to deform and permits the body to sink into the
surface, reducing pressure on bony prominences. Adequate air volume is
maintained with inflation or re-inflation devices. Gel mattress overlay have a
tissue life composition that reduces shear and support weight without
bottoming out. They are self sealing if punctured and can be reused. However,
gel does not deform easily and may become stiff overtime.
Group II: These surfaces are classified into dynamic powered
surfaces and advanced non powered surfaces. Dynamic air overlays are used
with mechanical pump to alternate inflation and deflation of chambers and
constantly change pressure points. Air chambers must have enough depth and

27. 34
be close enough together to lift the body during alternate cycles (McLeod
1997; Grindley and Acres 1996).
Group III: These consists of air fluidized beds, a high air loss
system with ceramic silicon beads that become fluidized as warm pressurized
air is forced up through the beads. This gives the beads the characteristics of a
fluid, allowing the patient’s body to float on the surface and minimize the
pressure, shear and moisture (Whittemore 1998; Hargest 1969).
2.7.1.1 Cover Materials Used in Support Surfaces
Cover material is an important element of support surface. Pressure
ulcers not only result from loads normal to the body surface, but also from
loading in the plane of the skin and the micro climate at the interface between
the subject and mattress. The choice of cover material significantly influences
these factors. Normal forces, primarily, weight is taken by both deformation
of the support structure, e.g., foam top surface and the elastic stretching of the
cover material. If the cover material is relatively in elastic, then more of the
load is taken by the cover in the plane of the skin. And this tends to have
shear effect on the skin. This form of loading can significantly contribute to
the development of pressure ulcers (Shaw 1997).
Damien et al (2004), estimated the effectiveness of a new high-
performance Australian medical sheepskin (meeting Australian Standard
4480.1-1998) in preventing pressure ulcers in a general hospital population at
low to moderate risk of pressure ulcers and found that the Australian Medical
Sheepskin is effective in reducing the incidence of pressure ulcers in general
hospital inpatients at low to moderate risk. The Canadian Association of
Wound Care puts forward 12 recommendations for best practices in the
prevention and treatment of pressure ulcers that focus on an interdisciplinary
patient-centered approach.

28. 35
Elizabeth et al (2002) interpreted on to what extent the pressure-
relieving cushions, beds, mattress overlays and mattress replacements reduce
the incidence of pressure ulcers compared with standard support surfaces and
how effective are different pressure-relieving surfaces in preventing pressure
ulcers, compared to one another and suggested that for people at high risk of
pressure ulcer, higher specification foam mattresses rather than standard
hospital foam mattresses should be used. Ken Dolynchuk et al (1992) reported
much higher pressure sore prevalence rates in the intensive care unit (ICU)
than the general hospital population.
2.7.1.2 Measurement of Interface Pressure, Temperature and Shear
Analysis of support surfaces has been carried out by various
authors (Rithalia 2005; Pring and Milman 1998, Trandel and Lewis 1975).
Steven et al (2002) studied the support surface interface pressure and
analyzed the role of implicated factors such as pressure, temperature,
moisture, shear and friction in the breakdown of the body wall tissues that
leads to pressure ulcer.
Hugo Partsch (2005) carried out sub-bandage pressure difference
measurement between active standing and lying in vivo using Kikuhime
pressure sensor. Eric Van den Kerckhove et al (2006) investigated the
reproducibility of repeated measurements with the Kikuhime pressure sensor
under two different types of pressure garments used in the treatment and
prevention of scars after burns. Narendar Reddy et al (1984) reported about
two types of semiconductors/transducers and two types of pneumatic
transducers used in clinical measurement of skin-cushion interface pressures.
Brian et al (2006) used a device which is composed of 80 transducers
arranged in an 8 × 10 array. Vert Mooney (2008), considered the effects of
seated posture and body orientation on the pressure-distribution and surface
shear (tangential) forces acting at the body seat interface.

29. 36
2.8 HUMAN COMFORT PROPERTIES
The term comfort is defined as "the absence of unpleasantness or
discomfort". There is general agreement that the movement of heat and water
vapour through a garment is probably the most important factor in clothing
comfort. (Slater 1977). The clothing comfort can be divided into three groups,
psychological, tactile and thermal comfort. Psychological comfort is mainly
related to the aesthetic appeal. Tactile comfort has a relationship with fabric
surface and mechanical properties.
Thermal comfort is related to the ability of fabric to maintain the
temperature of skin through transfer of heat and perspiration generated with
the human body (Hatch 1983). Two aspects of wear comfort of clothing are,
(i) thermo physiological wear comfort which concerns the heat and moisture
transport properties of clothing and the way that clothing helps to maintain the
heat balance of the body during various level of activity, and (ii) skin
sensational wear comfort which is based on the mechanical contact of the
fabric with the skin, its softness and pliability in movement and its lack of
prickle, irritation and cling when damp.
2.8.1 Clothing Comfort
Today comfort is considered as fundamental property when a
textile product is valued. The comfort characteristics of fabrics mainly depend
on the structure, types of raw materials used, weight, moisture absorption,
heat transmission and skin perception. Basically, clothing comfort can be
categorized under two broad components, viz, sensorial comfort and non-
sensorial comfort.
Sensorial comfort is a perception of clothing comfort which is
sensory responses of nerve endings to external stimuli including thermal,

30. 37
pressure, pain, etc producing neuro-physiological impulses which are sent to
the brain. Non-sensorial comfort basically deals with physical processes
which generate the stimuli like heat transfer by conduction, convection, and
radiation, moisture transfer by diffusion, sorption, wicking, and evapouration.
The heat and moisture transfer behavior of clothing has been studied
intensively by Fourt and Hollies (1970); Hollies and Goldman (1977).
2.8.2 Factors affecting Comfort
A number of properties of fibers, yarns, fabrics and garments are
significantly related to comfort and must be taken into account in producing
suitable apparel items. However, suitable fabrics, from the comfort point of
view, must be developed by textile technologists by proper selection of fiber
content, yarn and fabric construction techniques, and finishing treatments as
they influence physiological comfort level through thermal retention or
transmission etc. (Kothari 2004).
For getting thermo physiological comfort the clothing should
have suitable thermal conducting properties as well as sufficient permeability
to water vapour and / or sufficient level of ventilation (Jeffries 1990). The
textile structures can be developed to enhance the clothing comfort by
focusing principally on the thermal and mechanical properties (Prabhakar
Bhat and Bhonde 2006).There is general agreement that the movement of heat
and water vapour through clothing are probably the most important factors in
clothing comfort.
Rees (1972) concludes that the overall comfort of an apparel fabric
depends on the proper combination of values for pore size, air permeability,
water vapour permeability, thermal insulation, surface contact with skin and
several other fabric properties. Thermal wear comfort is mainly related to the
sensations involving temperature and moisture. (Prabhakar Bhat and Bhonde

31. 38
2006). It has been recognized for a long time that it is difficult to describe
comfort positively, but discomfort can be easily described in such terms as
prickle, itch, hot and cold. Therefore, a widely accepted definition for comfort
is ‘freedom from pain and from discomfort as a neutral state’ (Hatch 1983).
A core body temperature of approximately 37° C is required by an
individual for his well being. Hence, the body temperature is the most critical
factor in deciding comfort. Heat is gained by the body from the sun or
intermediate source of energy, by internal metabolism, physical exercise or
activity, or by involuntary contractions of skeletal muscles in shivering
(Prabhakar Bhat and Bhonde 2006). Li and Holcombe (1998) developed a
mathematical model to describe the dynamic heat and moisture transport
behavior of clothing and its interaction with the human thermoregulation
system under transient wear conditions.
Sheela Raj and Sreenivasan (2009) carried out an in depth study to
understand fabric handle and wear comfort in relation to fiber, yarn and fabric
structural parameter and presented a comprehensive grading index
incorporating the air permeability, moisture and thermal transport of the
fabric. Combining different parameters responsible for thermo physiological
and tactile comforts by conferring different weighting factors, a pair of
indices of comfort have been defined viz. Thermo Physiological Comfort
Index (TPCI) and Total Wear Comfort Index (TWCI). These indices are
expected to provide a practical way for assessing overall wear comfort.
Roger L Barker (2002) discussed the evolution of objective
measurement of textile hand and comfort from Pierce through modern
methodology and approaches. Special emphasis is given to the contribution of
the Kawabata Evaluation System (KES) towards advancing the state of
objective measurement.

32. 39
2.9 AIR PERMEABILITY OF FABRICS
The concept of ‘air permeability’ is widely used in the textile
industry to interpret the intrinsic characteristics of fabric. Air permeability is
significantly influenced by a fabric’s material and structural properties, such
as shape and value of the pores of the fabric and yarn, which in turn are
dependent on the structural parameters of the fabric, such as fabric weave, the
raw material of the yarns, the set of yarns and others. In addition, as the
results of McCullouh et al’s (2003) research show, fabrics with hydrophilic
components can change their air permeability properties under different
humidity conditions.
The application of permeability tests to textile products as well as
determining permeability and porosity has long been subjects of interests
(Berkalp 2006). The so called clean room textiles protect an atmosphere
against particles emitted from human body and vice versa, also provide
protection against particles evolved from clothing (Militky et al 1999). Air
permeability being biophysical feature of textiles determines the ability of
fabric to carry out gaseous substances, significantly influences thermal
comfort of the human body, secure the support of the proper body
temperature (Frydrych et al 2003). Air permeability (Stankovic 2005) along
with other comfort properties of hemp textiles for hospital uses was
investigated.
It was determined that nonwoven fabric weight is more important
parameter for air permeability if to compare with thickness, fiber diameter,
and density (Kothari and Newton 1974). Daukantien and Skarulskien
(2005) stated that the air permeability increased with the increase of porosity
of the fabric or decrease of its thickness. The use of spacer fabrics with air
supported layer for excellent air permeability and thermoregulation was
interesting textile-technological solution for medical applications (Heide et al

33. 40
2005). Renata Baltakyt and Salvinija Petrulyt (2008) indicated that air
permeability was a function of knitted fabric thickness and surface porosity.
2.9.1 Air Transfer
Moisture movement and air movement through a textile fabric are
sometimes considered together under the topic of fluid flow. Air flow is
similar to diffusion of moisture vapour through a textile fabric. Air flow
through a fabric occurs when the air pressure is different on the two sides of
the fabric. It is closely related to convective heat transfer and to moisture
transport via diffusion. As fabric interstices increase in number and size, air
permeability increases.
Alibert (1972) investigates the air permeability of fabrics in relation
to structure and establishes the general laws governing the filtration of air
through his test samples. Kretsschmer (1973) introduces a ‘structure index’ to
simplify the use of his earlier permeability equation for textile materials in a
flat, single-layer configuration and gives examples to demonstrate the use of
the modified equation with his index included.
Renata Baltakyt (2008) carried out experimental investigations for
determining air permeability dependence on weave. The weft setting has a
very great influence on fabric air permeability but in the case of the same
firmness factor this influence is negligible and Q is constant for all weaves.
So, it is possible to reach constant air permeability for fabrics with different
settings by choosing a necessary weave for each setting.
2.9.2 Porosity and Cover Factor
The pores, or interstices within a fabric, are also influential factors
in moisture and air transfer. Volume porosity of a fabric is defined as the ratio

34. 41
of the volume (fabric plus air or void) expressed as a percentage (Adanur
2006, Berkalp 2006). Apparent porosity of a fabric is the air porosity which
has the same meaning as air permeability (Booth 1968; and Benltoufa et al
2007). Skinkle (1949) defines porosity as the ratio of air space to the total
volume of the fabric expressed as a percentage. The type of finish given to a
fabric can have a considerable effect on the permeability even though the
porosity may remain the same. A roughly identical method of calculation was
presented by Hsieh (1995).
A term that is closely related to porosity is cover factor. Cover
factor combines fabric count and yarn size to give an indication of fabric
structural properties that contribute to thermal comfort. However, the term
cover factor does not take into consideration of other structural factors such as
yarn type or yarn twist (Billie and Helen 1999). Knitted structures generally
have more porosity that can retain more air and therefore provide more
warmth (Richard 2005).
2.10 Moisture Management in Fabrics
An important property associated with fabric comfort is moisture
management. Moisture management deals with the ability of a fabric to
transmit moisture away from the body. The mechanism of movement can be
either by wicking or by passage of water vapour through the fabric.
Breathability is a term often used to describe this property. The term
‘moisture management’ always refers to the transport of moisture vapours and
liquid away from the body.
The most important factors affecting moisture transfer are fiber
type, cloth construction, weight or thickness of the material, presence of
chemical treatments. In the case of cotton, the hydrophilicity of the fiber itself
wicks away the moisture, which passes through the openings in the fibers or

35. 42
yarns, where distinctly accelerated evapouration takes place, resulting in
comfort for the wearer. On the other hand, clothing made up of synthetics
such as polyester or polyamide, etc, is unable to wick away the
moisture/perspiration due to their inherent hydrophobic nature, so the fabric
tends to stick to the skin, which impairs the comfort. To maximize comfort
and to feel cool in synthetic garments, the fabric must allow liquid to wick on
to the surface, spread away and evapourate quickly. The ability of soil release
finishes to improve water wicking also serves to improve moisture
management and is often promoted as finishes for improved comfort (Behery
2005).
The dissipation of perspiration and body heat is also influenced by
the porosity and wicking characteristics of apparel fabrics. Pore size affects
air resistance and water repellency. Usually, the larger the pore size, the lower
the resistance to air flow and the lower the water repellency. Wicking
efficiency is affected by fabric geometry of fibers in yarn and fabric. Usually,
hairiness and random fiber arrangement lead to slow rates of wicking and
surface wetting (Rees 1972).
2.10.1 Liquid Moisture Transfer: Capillarity, Wetting and Wicking
The primary cooling mechanism of the human body is evapouration
of perspiration, with water vapour carrying heat away from the body as it
evapourates out of the skin’s pores. In the garment-skin microclimate
environment, the absorption of sweat by garment and its transportation
through and across the fabric where it is evapourated are claimed by some
researchers to aid clothing comfort perception. The manner of the moisture
absorbed at the fabric inner surface, transported between the two sides and
evapourated at the outer surface significantly influences the wearer’s comfort
sensation, as the moisture is a much better heat conductor than air.

36. 43
Capillarity can be defined as the macroscopic motion of a liquid
under the influence of its own surface and interfacial forces in narrow tubes,
cracks, and voids. The surface tension is based on the intermolecular forces of
cohesion and adhesion. When the forces of adhesion between the liquid and
the tube wall are greater than the forces of cohesion between the molecules of
the liquid, then capillary motion occurs. Flow ceases when the pressure
difference becomes zero.
Wicking in fabrics may occur in a range of conditions and
situations. Ghali et al (1994) believes that “to define the range of conditions,
researchers should attempt to distinguish between two phenomena, namely
wettability and wickability, related to liquid transport in fabrics”. According
to Harnet and Mehta (1984) “wickability is the ability to sustain capillary
flow” whereas wettability describes the initial behaviour of a fabric, yarn or
fiber when brought in contact with water.
Wetting is the displacement of solid - air interface with a solid-
liquid interface. Spontaneous wetting is the migration of a liquid over a solid
surface towards thermodynamic equilibrium. Wetting and wicking are not
different processes. Wetting is a prerequisite for wicking. A liquid that does
not wet fibers cannot wick into a fabric. When the fibers in assembly are
wetted by a liquid, the resulting capillary forces drive the liquid into the
capillaries created by the spaces between fibers in wicking process.
In general wicking takes place when a liquid travels along the
surface of the fiber but is not absorbed into the fiber. This type of flow is
governed by the properties of the liquid - solid surface interactions, and
geometric configurations of the pores structure. The pores structure of a
fibrous medium is complicated and difficult to quantify. Moreover with
hydrophilic fibers, the swelling of fibers influences the liquid flow.

37. 44
Erik Kissa (1996) reviewed the fundamentals of wetting and
wicking. Wetting is the displacement of a fiber-air interface with a fiber-
liquid interface. Wicking is the spontaneous flow of a liquid in a porous
substrate, driven by capillary forces. You-Lo-Hsieh (1995), discussed wetting
and capillary theories and applications of these principles to the analysis of
liquid wetting and transport in capillaries and fibrous materials. Hollies et al
(1957) made a basic study of the mechanism of water transport in yarns and
found that the movement of water along fabrics is shown to depend on the
laws of capillary action and the water is carried mainly in the capillaries
formed by the fibers in the individual yarns. The speed of travel of water in
these capillaries is readily reduced by the presence of randomly arranged
fibers in the yarn, and it is this factor rather than the nature of the fiber
material which accounts for the wide range of water transport properties
found in blended fabrics.
2.10.2 Moisture Transport in Different Fibers
Cotton: Cotton garments provide a good combination of softness
and comfort. However, cotton is not recommended for use in base layer
clothing because of its tendency to absorb and retain moisture. When wet,
cotton garments cling to the skin and cause discomfort. The slow-to-dry and
cold-when-wet characteristics of cotton make this material unsuitable in
conditions in which there are high levels of moisture-either perspiration or
precipitation and where the ambient temperature is low.
Cellulosic fibers: Cellulosic fabrics absorb water into the fiber
structure and become heavy. This leads to stretching of the fabric, sticking to
the skin and when activity ceases the fabric may feel cold against the skin.
Higher levels of moisture absorbed in the fabric mean longer drying times.
However, cellulosic fabrics are generally perceived to be more comfortable
than synthetic fabrics when worn for normal day-to-day activities.

38. 45
Viscose Rayon: The outer layer of knitted hydrophilic portion of
the twin layer sportswear can be of viscose rayon, which absorbs 2-3 times
more moisture than cotton. The wicking behavior improves by incorporation
of some hydrophobic finishes. However, if it were blended with polyester, the
absorbent capacity could be controlled to an acceptable level.
Comfort properties of polyester microfiber fabric are more in terms
of wicking when compared with polyester micro/cotton blends and pure
polyester non- micro fiber fabrics. Better wicking is found in samples having
greater proportion of polypropylene and they dry fast. Maximum water
vapour permeability and air permeability is seen on fabrics having
polypropylene on both faces of fabrics.
Toray developed a fabric made from polyester filament yarn which
has grooves which help the fabric absorb sweat quickly and disperse it along
the surface. Polyester coolmax has been claimed to increase wearer comfort
through rapid removal of perspiration by capillary. Also it has good wicking
properties and no absorbency.
Using a series of manikin and human subject experiments, Crow
and Osczevski (1998) examined the interaction between water and a range of
fabrics to investigate claims that synthetic fibers such as polypropylene do not
pick up moisture. They found that all fiber types, when made into fabrics,
pick up water, with a strong correlation between a fabric’s thickness and the
amount of water it picks up, freely expressed in absolute terms rather than as
a percentage of its mass. The amount of water wicked from one layer to
another depends on pore sizes and their corresponding volumes. While most
fabrics, both natural and synthetic have the ability to wick moisture from the
skin, not all of these are fast drying and air permeable – two factors, which
have a direct influence on cooling and perceived comfort. High tech synthetic

39. 46
fabrics are light weight, are capable of transporting moisture efficiently and
dry relatively quickly.
It is generally agreed that fabrics with moisture wicking properties
can regulate body temperature, improve muscle performance and delay
exhaustion. While natural fibers such as cotton may be suitable for low levels
of activity, synthetic fibers made of nylon or polyester are better suited for
high levels of activity. They absorb much less water than cotton, but can still
wick moisture rapidly through the fabric.
Manas Sarkar et al (2009) developed a textile fabric simulating a
plant structure with superb liquid water transport properties. He developed
some novel weave structures, which emulate the branching structures of the
plants and create a continuous water transport passing from the bottom layer
to the top layer by interchanging the yarns from the bottom layer to the top
layer. The connecting weave has an influence on capillary rise. Fabrics
without connecting weave have the smallest wicking coefficient. When the
density of connecting crossing is increased, wicking coefficient increases.
Shinjung Yoo and Roger Barker (2005) found that Heat-resistant
fabric incorporating structural features that minimize skin contact, while also
providing liquid absorption capacity, are predicted to show enhanced comfort
performance. Blending of hydrophilic fibers and wicking finishes, however,
do not necessarily improve the comfort perceptions in the tested scenarios.
Junyan Hu et al (2005) devised a new method and instrument called
the moisture management tester to evaluate textile moisture management
properties which could be used to quantitatively measure liquid moisture
transfer of a fabric in multi directions. Hasan et al (2008) elucidated that
topographical characteristics of the fabrics strongly depend on their

40. 47
construction parameters such as the type and fineness of filaments, yarn
fineness, yarn density, and consequently, the type of weave.
Brojeswari Das et al (2008) states that the moisture transmission
behavior of a clothing assembly plays a very important role in influencing its
efficiency with respect to thermo physiological body comfort. Part I of their
paper deals with the processes involved in moisture transmission and the
factors at play. Part II is concerned with selecting the measurement
techniques which are of great importance in determining fabric factors that
influence comfort. Brojeswari Das et al (2008) carried out an experimental
study on the effect of fiber cross sectional shape and fiber diameter on
moisture transmission properties of the fabric. With the change in shape
factor, fiber diameter and increase in fiber specific surface area, wicking rate
through fabric increases, whereas water vapour permeability of the fabric
reduces. Jakub Wiener and Petra Dejlová (2003), proposed a model of
wicking based on the simplified description of the thread structure
considering the parameters like fineness of fibers, and number of fibers at the
cross-section in the bundle and the filling.
Petrulyte and Baltakyte (2009) carried out investigations in liquid
sorption and transport for three different variants of terry woven structures.
The study carried out by Kothari and Kausik Bal (2006) established a new
approach to determine the blend proportion in polyester-viscose blends in
woven fabrics. A new rapid conditioning method by drying the samples with
infra-red and then conditioning them for a shorter duration was used to
compare the moisture content values of different blend levels. In all cases, the
moisture content values showed linear relationships with the proportion of
viscose in the fabrics.
Adler and Walsh (1984) developed a technique to study moisture
transport and made an effort to determine the mechanism by which moisture

41. 48
is transported between fabrics under transient conditions at low moisture
contents. Wicking did not begin until the moisture content was high, more
than 30% above regain for the woven samples. Crow and Osczevski (1998),
examined the interaction between water and a range of fiber types and found
that, when made into fabrics, all fabrics pick up water, with a strong
correlation between a fabric's thickness and the amount of water it picks up
freely expressed in absolute terms rather than percent of its mass.
Scheurell et al (1985) tested the Dynamic surface wetness of fabrics
and found a correlation with skin contact comfort in wear for a variety of
fabric types and suggested that mobility of thin films of condensed moisture is
an important element of wearing comfort. Sukigara et al (1997) made an
investigation into the sensation of wetness and dampness by both subjective
and objective measurements.
2.11 DRYING TIME OF FABRICS
Drying time is the time required to evapourate water from a wet
fabric, which depends on the amount of water the fabric picks up, not the fiber
type. Raechel M. Laing et al (2007), developed a laboratory method for
wetting specimens and determining drying time and defined end-point ‘dry’,
applicable to a wide variety of apparel fabrics and made an effort to determine
the drying time of a range of apparel fabrics simulating both during and after
wear conditions using a simulated on-skin drying method.
Prahsarn et al (2005) used a test method that measures
microclimate drying time to compare the ability of different knit materials to
dissipate moisture vapour from a saturated clothing environment to the
ambient atmosphere. The thickness of fabric and the pore characteristics of
the fabric determine the drying rate.

42. 49
Shinjung Yoo and Roger (2005) analyzed the moisture
management properties of heat resistant workwear fabrics and the effects of
hydrophilic finishes and hygroscopic fiber blends using a demand wettability
test and found that the cotton fabric shows the highest percentage of
remaining water after the evapouration test, a garment made of this fabric may
generate a clammy feeling despite its superior absorbent capacity and rate of
absorption.
2.12 WATER VAPOUR TRANSMISSION BEHAVIOR OF FABRICS
The water vapour permeability of a given material plays an
important role in evaluating the physiological wearing comfort of clothing
systems or in determining the performance characteristics of textile materials
used in technical applications. Water vapour condensation occurs when air
space size is very small, say 5mm. In such cases, water vapour permeability
has more effect on heat and mass transfer than air permeability. Vapour
permeable fabrics have a relatively lower amount of condensation heat flux
than vapour-impermeable fabrics. In other words, such a fabric can keep the
temperature and the amount of absolute water vapour concentration in the
microclimate, low. High values of these cause sensations of humidity and heat
stress in the wearer.
Wang and Yasuda (1991) developed a new experimental apparatus
for studying the transport of water vapour and liquid water through textile
fabrics during the transient period and also proposed two experimental
methods in their paper: the water vapour method and the sweat method.
Indushekar et al (2005) evaluated the water vapour transmission of a wide
range of base fabrics used in extreme cold weather protective clothing using
the conventional Dish and MDSC techniques.

43. 50
Akshaya Jena and Krishna Gupta (2002) augmented a novel
technique for precise, accurate and fast determination of vapour transmission
rate through textiles. Vapour at a constant pressure is maintained on one side
of the textile and the increase in pressure of the vapour on the other side is
measured. The vapour permeability of the textiles is almost five orders of
magnitude lower than their air permeability.
Fourt et al (1957) measured the water vapour transmission of fibers
independent of any air space surrounding the fibers, by using sections cut
from embodiments of the fibers in polyacrylic resins. The rate of water
vapour transmission, measured as the diffusion constant, is larger for cotton
than for Rayon, Wool, Nylon and Dacron. The respective diffusion constants
are on the order of 134, 56, 39 and 8 respectively.
Scheurell et al (1985) found a correlation between dynamic surface
wetness of fabrics and skin contact comfort in wear for a variety of fabric
types, suggesting that mobility of thin films of condensed moisture is an
important element of wearing comfort. Although much study has been
dedicated to heat and water vapour transport through fabrics, there remains a
great lack of understanding on water vapour transport through fabrics under
subzero climate, particularly in terms of the effect of condensation on water
vapour transport. Xiaohong Zhou et al (2006) reported a novel apparatus,
used to measure the moisture transport through fabrics under a conventional
(20°C) and subzero (-20°C) climatic condition.
Raechel M. Laing et al (2007) developed a model of heat and water
transfer through layered fabrics by considering few special properties such as
hydrophobic, hydrophilic treatment and surface modification of textiles.
Chuang Li et al (2005) pioneered a new type of fabric micro environment
testing instrument to measure the dynamic changes of vapour pressure,
temperature, and heat flux under simulated human body sweating conditions.

44. 51
2.13 THERMAL COMFORT PROPERTIES OF FABRICS
Thermal properties of textile materials especially thermal
conductivity have always been the major concern when the comfort properties
of clothing are concerned. Clothing has a large part to play in the maintenance
of heat balance, as it modifies the heat loss from the skin surface and at the
same time has the secondary effect of altering the moisture loss from the skin.
The properties of clothing materials critically influence the comfort and
performance of the wearer. Clothing is not just a passive cover for the skin. It
interacts with and modifies the heat regulating function of the skin and its
effects are modified by the environment. Thermal conductivity and thermal
insulation or thermal resistances and thermal absorptivity are few measures of
thermal comfort.
2.13.1 Thermal Conductivity
The ability of a fabric to conduct heat through it is of critical
importance to its thermal comfort. Thermal conductivity is a property of
materials used to describe the thermal transfer behavior of the heat flow
through a fabric due to a combination of conduction and radiation where the
convection within a fabric is negligible. The conduction loss can be
determined by the thickness of the fabric and its thermal conductivity. As
defined by ASTM, thermal conductivity is the time rate of unidirectional heat
transfer per unit distance, per unit difference of temperature of the planes.
Another relevant concept is thermal conductance (C), also defined by ASTM
as the time rate of heat flux through a unit area of a body induced by unit
temperature difference between the body surfaces. Normally thermal
conductivity can be expressed in equation 2.1
L/T
A/Q
k (2.1)

45. 52
Where Q is the amount of heat passing through a cross-section A,
causing a temperature difference T , over a distance of L . Q/A is therefore
the heat flux which is causing the thermal gradient. The measurement of
thermal conductivity, therefore, always involves the measurement of the heat
flux and temperature difference. The difficulty of the measurement is always
associated with the heat flux measurement. Guarded hot plate, as described in
ISO 8302, is a widely used and versatile method for measuring the thermal
conductivity of textiles. Another widely used simple method is directly using
a heat flow meter as described in ASTM C 518.
2.13.2 Thermal Insulation
Thermal insulation property of the fabric refers to the ability to
resist the transmission of heat by all modes. It can also be defined as
effectiveness of a fabric in maintaining the normal temperature of the body
under equilibrium conditions. The most important thermal property in most of
the apparels is the insulation against heat flow, which is measured by thermal
resistance. It is defined as the ratio between temperature difference between
the two faces and heat flux.
The thermal resistance, R and thermal conductivity, K are related as
follows,
R = d /K (2.2)
Where d is the thickness of the material. Since K is roughly
constant for different fabrics, hence thermal resistance is approximately
proportional to fabric thickness. Thermal insulation value is higher in case of
silk fabric compared to cotton fabric. It is due to openness of knit structure of
silk fabric. Silk fiber contains higher thermal insulation value as it has lower
thermal conductivity (50 mw/m/k) than cotton (71 mw/m/k).

46. 53
In studying the thermal insulation properties of garments during
wear, it is reported that thermal resistance to transfer of heat from the body to
the surrounding air is the sum of three parameters: (i) the thermal resistance to
transfer heat from the surface of the material, (ii) the thermal resistance of the
clothing material and (iii) the thermal resistance of the air interlayer. It is
obvious that heat transfer through a fabric is a complex phenomenon affected
by many factors. The three major factors in normal fabrics appear to be
thickness, enclosed still air and external air movement. Out of which, the
entrapped air is the most significant factor in determining thermal insulation.
There are "microlayers" (those between contacting surfaces of the materials)
and "macrolayers" (between non-contacting surfaces) of air enclosed within
an assembly and an increase of either of these can increase thermal insulation.
However, the characteristics of fiber, yarns, fabrics and garment assemblies
have also a major contribution towards thermal comfort.
Most textile fibers are poor conductors of heat, but air conducts
even less heat. If air is confined in small spaces, then convection is also
minimized, and the air is ‘dead’. The higher the volume of dead air within a
textile structure, the lower the thermal transmittance, therefore, the better the
insulation value of the textile material. (Billie and Helen 1999).
2.13.3 Mechanism of Heat Transfer
To understand the thermal properties of the textile system, it is
necessary to assess the contributions of the various heat-transfer mechanisms
that may be operative. These mechanisms are conduction, convection and
thermal radiation for dry heat transfer (Gagge et al 1941; Rohsenow 1973).
2.13.3.1 Conduction
Fibers and air intermingle together in any textile yarns and fabrics
hence the fabrics are neither homogeneous nor isotropic. However, with the

47. 54
preposition that the average heat-transfer properties of fabrics are to be
measured and calculated through the theoretical and practical work, it is
reasonable to assume that a fabric is a homogeneous and isotropic material in
heat transfer. In addition, since thickness of a fabric is substantially smaller
than the fabric width and length in normal clothing situations, it is also
feasible to consider the heat transfer through a fabric is a one-dimensional
problem. Under such assumptions, the transient heat-transfer process through
the insulating material is described as in Equation (2.3), (Yang and Tao
1999).
2
2
.
x
T
cpt
T
(2.3)
Where, T temperature (°K);
t time (s);
conductivity (W m -1
K -1
);
mass density (kg m -1
);
c specific heat (W S kg -1
K -1
); and
x direction of heat transfer.
2.13.3.2 Convection
As one of the basic heat-transfer mechanisms, convection involves
the transport of energy by means of the motion of the heat-transfer medium,
in this case the air surrounding the human body. When cold air moves past a
warm body, it sweeps away warm air adjacent to the body and replaces it with
cold air. It has been found that there is no convection inside clothing
insulation even with a very low density (Peirce and Rees 1946). In the FE
analysis, the convective heat transfer will be set as a boundary condition. The
heat flux due to convection can be expressed as follows (Incropera and
DeWitt 2002):

48. 55
)( xr TThq (2.4)
Where, q heat flux (W m -2
);
h film coefficient (W m -2
K -1
);
T out surface temperature of the fabric (°K); and
T temperature of the ambient atmosphere (°K).
2.13.3.3 Radiation
The heat loss carried out by radiation from a clad human body to
the environment is a situation where the clad human body as the heat source is
enveloped by the environment. In this case, the heat flux by radiation at the
outer surface of the textile assembly is governed by the following equations
(2.5) and (2.6)( Incropera and DeWitt, 2002).
)TT(q 4
x
4
r
(2.5)
)TT()TT(h
n
y 4
x
4
rxr
(2.6)
Where,
Stefan-Boltzmann constant, which is 5.6703×10-8
W m-2
K-4
; and
emissivity of the surface.
2.13.4 Heat transfer through Textiles
Heat transfer through a textile assembly or a fabric system is a
complex process, involving conduction, radiation and convection. The
combined heat transfer across the fabric system, consisting of fabric and air
layers, is not simply the sum of what each mechanism would do in the
absence of the others. The three heat transfer mechanisms work together to
determine the characteristics of the overall heat transfer process.

49. 56
Heat transfer refers to the transfer of heat energy from one
environment to another. Heat transfer occurs whenever a temperature
difference ( T) exists between the two environments; heat moves from the
warmer surface or area to the cooler surface or area. Heat transfer will
continue until the two areas attain same temperature (at equilibrium). The rate
at which heat is transferred depends on T as well as any resistance imposed
between the two environments. For people, this means that if the ambient
temperature is lower than the body temperature (37° C), heat will flow from
the body to the surrounding area. If the ambient temperature is higher than the
body, heat will flow the other way and the body will become warmer.
Clothing can provide resistance to heat transfer in either direction by serving
as insulation between the two environments (Billie and Helen 1999).
For clothing textiles, heat transfer is a complicated transient
process. Generated form the body, heat transfers through the air gap between
skin and fabric, then through the fabric system, to the outer surface of the
fabric system. During this process, conduction, convection and radiation are
all involved, may be to different extent, in determining the total heat loss.
Peirce and Rees (1946) pointed out that at the outer surface of the
clothing exposed to the air; heat is lost by means of both convection and
radiation. Farnworth (1983) presented a theoretical treatment of heat transfer
through a bed of fibers considering conduction and radiation and reported that
no detectable convective heat transfer took place inside the fiber bed. In a
more recent study, Mohammade et al (2003) presented a theoretical equation
of the combined thermal conductive, convective, and radioactive heat flow
through heterogeneous multi-layer fibrous materials.
Dul’nev and Muratova (1968) discussed heat transfer processes in
fibrous materials and derived formulae from which effective thermal
conductivity can be calculated from thermal, geometrical, and volumetric

50. 57
parameters of the components. Mitu and Potoran (1971) used a formula
derived by earlier workers for calculating the thermal resistance of clothing
to determine a series of values of this property that represent acceptable
comfort limits for the human body when engaged in lying, sitting, walking,
running and other such activities.
As long as the air within a fabric or fabric assembly is so called
‘dead’ air, it provides good resistance to heat transfer. However, as the
volume of air space increases, the likelihood of air movement, or convection,
increases. When convection occurs, it is usually the dominant mode of heat
transfer, overpowering any effects of reduced conduction of heat (Billie and
Helen 1999). Fibers have a high surface to volume ratio; thus there are many
small spaces for dead air within a fibrous structure. In those spaces, there is
little thermal transmittance because air is a very poor conductor of heat; and
there is little radiation because although air is transparent to radiation, fibers
are not (Billie and Helan 1999).
Pile or napped constructions are often good for cold weather
because the yarns or fibers perpendicular to the surface provide numerous
spaces for dead air. This effect is maximized when such fabrics are worn with
the napped or pile surface next to the body, or when they are covered with
another layer. Otherwise, the protruding fibers in the nap structure may
conduct heat away from the body (Billie and Helen 1999).
Fabric construction also influences thermal insulation. Knitted
fabrics generally have a soft hand and higher heat-retaining properties
compared with that of woven fabrics of a specific thickness or weight. Knits
usually entrap more air than woven fabrics, although the tightness of the
weave or knit is a factor as well. In addition to the openness of the structure,
other fabric characteristics are influential in thermal insulation.

51. 58
Heat transfer through a textile assembly consisting of fabric and air
layers can be calculated based on a theoretical model capable of dealing with
conductive, convective and radioactive heat transfer. The size of the air gaps
has a significant influence on the heat transfer. The balance heat flux drops by
40 per cent when the air gap increases from 2 to 10 mm. The influence of the
air gap tends to become smaller as the air gap is further increased. The
number of fabric layers in the textile assembly has a noted influence; more so
when the ambient temperature is lower (Yuchai Sun et al 2010).
2.13.5 Measurement of Thermal Properties Using Thermal Manikin
Since the first one segment copper thermal manikin in the world
was made for the US army in the early 1940s, more than 100 different thermal
manikins have been employed for research and product development
worldwide. Holmer (2004) reviewed thermal manikin development history
and summarized the milestones. Interest in using thermal manikins in research
and measurement standards is steadily growing and several international
testing standards have been developed in the field of the thermal comfort
evaluation.
To date, thermal sweating manikins are widely used in large scale
textiles and clothing research laboratories all over the world for analyzing the
thermal interface of the human body and its environment. Normally, the
thermal manikin is made from metal or fabric e.g. copper, plastic or water /
windproof fabric with an independent controllable heating/sweating
subsystem, data measurement and analyzing subsystems. With the
development of computer and computation technologies, visual realization
models have become more and more important and are now widely applied in
the field of thermal comfort estimation. Li et al (2004) developed a computer
based model for studies of heat moisture transfer in clothing systems. Buxton
et al in the UK are also developing a similar model that allows the use of

52. 59
human body data from whole body scanners and motion patterns derived from
real recordings.
The thermal/sweating plate has been used for years to determine the
thermal and moisture resistance properties of fabrics. The applications and
description of sweating hot plates can be found in literature by Kawabata et al
(1977) and Holmer (2007). There are several types of skin model employed in
clothing comfort research. Kawabata reported the application of hot plate
technology for the measurement of fabric warm and cool feelings. Typical
structure and detailed description of a sweating hot plate can be found in ISO
11902-1993(E). Another newly developed apparatus is the Dynamic Sweating
Hot Plate, which was developed by NCSU and can be used to measure the
thermal capacity of fabrics under different humidity conditions.
2.13.6 Effects of Clothing Material on Thermoregulatory Responses
Today the technology applying micro PCMs (about 3 million
capsules per cm2
) to the fabrics have been achieved and the microcapsules are
added to fabrics by a conventional pad-dry-cure process. Kyeyoun Choi et al
(2004) applied Melamine formaldehyde microcapsules containing octadecane
are synthesized by the interfacial polymerization method, and the size, shape,
and thermal storage/release properties of the synthesized microcapsules are
analyzed by FTIR, SEM, and DSC and found that under the optimum
treatment concentration, temperature, and time, thermal properties after five
launderings decrease rapidly.
Nilgunozdil et al (2007) observed that yarn properties like yarn
count, yarn twist and combing process of cotton have affected different
thermal comfort properties of 1×1 rib knitted fabrics. Jintu Fan and Xiao-Yin
Cheng (2005), reported on an experimental investigation on the effect of
clothing thermal properties on the comfort sensations of wearers during sport

53. 60
activities. A sweating manikin “Walter” was used to measure the clothing
thermal properties namely, thermal insulation, moisture vapour resistance and
moisture accumulation within clothing of five tracksuits made of 100%
polyester and 100% nylon and found that the thermal comfort sensations
during active sports wear is strongly related to the moisture vapour resistance
and moisture accumulation within clothing.
Damjana Celcar et al (2007) presented a development concept of
the mathematical model enabling an objective evaluation of the human
thermal comfort by simulation of the heat transfer from the human body to the
ambient air. Based on the simulation results, it can be concluded that the
numerical solution is able to predict heat transfer from the human body to the
ambient air.
Direct measurement of the convective and radiative heat transfer
coefficients from the clothed human body to the environment is important in
all work requiring knowledge of the human heat balance. Such measurements
can be achieved using a specially designed garment that incorporates heat flux
sensors. Sensors mounted in pockets were calibrated using a guarded hot plate
facility. Geraldes et al (2008) presented an engineering design of the principal
thermal properties in functional structures and proposed three new equations
that simulate the reality of the behaviour of the knitted structures.
Chen et al (2003) tested clothing thermal insulation on a novel
fabric thermal manikin covered with lightly breathable and highly breathable
skins to simulate low and heavy perspiration respectively. Wu (2009) found a
new method of assembling different kinds of fabrics made of cotton, wool,
lyocell, modal, soyabean, bamboo and their blends to match different sections
of the human body to improve the thermal-wet comfort of the clothing system
during exercise. Jianhua Huang (2008) designed six models for determining
air temperatures for thermal comfort of people using sleeping bags. These

54. 61
models were based on distinctive metabolic rates and mean skin temperatures.
All model predictions of air temperatures are low when the insulation values
of the sleeping bag are high.
2.14 MULTILAYERED FABRICS
Multi layered fabrics consist of different layers of the fabrics which
has the ability to complement and maximize the essential comfort properties
for a specific end use. Various research works have been carried out to
analyze the functional properties of layered fabrics. Fohr et al (2002) have
simulated a mathematical model to determine heat and water transfer through
layered fabrics.
Guldemet Basal and Sevcan Ilgaz (2009) developed a functional
fabric for pressure ulcer prevention with a spacer fabric made of different
combinations of engineered polyester, polypropylene, cotton and viscose fibers
by face-to-face velour weaving technique and recommended the channeled
polyester, cotton and polypropylene as the most promising fiber types for
pressure ulcer prevention.
Sharabaty et al (2008) studied the wettability characteristics of
polyester, cotton and multilayered polyester/cotton fabrics to manage human
perspiration and found that wicking coefficient of multilayered fabrics is
better than cotton fabrics. Xiaohua Ye et al (2008) developed warp knitted
spacer fabrics from PES multifilament and monofilament yarns for cushion
applications and analyzed the pressure distribution, air permeability, and heat
resistance of the fabrics and concluded that these spacer fabrics could be used to
substitute PU foam, especially in the case where the comfort and recycling are
highly required.

55. 62
Yasuda and Miyama (2002) found that, when liquid water
contacted a fabric, such as in the case of sweating, the surface wettability of
fabric played a dominant role in determining the water vapour transport rate
through layered fabrics. Wang and Yasuda (1991) designed an experimental
apparatus to permit simultaneous measurement of temperature change and
moisture flux through fabrics during the transient period after one set of
fabrics has been exposed to humidity and temperature gradients.
Markus Weder et al (2004) used Neutron radiography to study
moisture transport in textiles for the first time. Jintu Fan and Xiao-yin cheng
(2005) investigated heat and moisture transfer through clothing assemblies
consisting of porous fibrous battings sandwiched by inner and outer layers of
thin covering fabric and found that the water content accumulates with time,
and water content is higher at the outer regions than at the inner regions of
battings. Zhuang et al (2002) investigated the liquid transfer from fabric layer
to layer and liquid interaction between different fabrics in clothing systems
and found that the amount of liquid transferred largely depends on the
performance of individual fabrics as well as the way in which they contact
each other.
Another new development is a performance enhancing fabric that
cools through evapouration. Designed with three layers, when soaked with or
immersed in water, the central layer absorbs and retains moisture. As the
water evapourates from this layer, the fabric cools the wearer while its shell
and lining keep the wearer dry. Production of this fabric starts with a super
water absorbing polymer fiber that is blended into fibrous matting. This
matting is positioned between a breathable exterior shell and a conductive
waterproof lining (Prabhakar Bhat and Bhonde 2006).
Pile or napped constructions are often good for cold weather
because the yarns or fibers perpendicular to the surface provide numerous

56. 63
spaces for dead air. This effect is maximized when such fabrics are worn with
the napped or pile surface next to the body, or when they are covered with
another layer. Otherwise, the protruding fibers in the nap structure may
conduct heat away from the body (Billie and Helen 1999).
Field sensor is a very popular high performance fabric from Toray,
which employs a multilayer structure that not only absorbs perspiration
quickly but also transports it up to the outer layer of the fabric very rapidly
using principle of capillary action. It is composed of coarser denier yarn on
the inside surface (in direct contact with the skin), and the fine denier
hydrophobic polyester yarn in a mesh construction on the outer surface to
accelerate quick evapouration of sweat (Yonenaga 1998).
Another multi layered fabrics developed using high-tech polyester
yarns with specially designed ‘W’ shape cross section speeds up fabric’s
ability to transport water away from the skin. Its increased surface area
increases the evapouration rate. So these fabrics exhibit quick drying
properties. Uncomfortable perspiration is rapidly absorbed and the skin
remains dry and more comfortable (Prabhakar Bhat and Bhonde 2006).
Another fabric developed is a light weight material consisting of Sun opaque
fiber at face side which contains a high density titanium core that blocks UV
rays and Polyester yarn with ‘W’ shape cross-section at the back side of the
fabric for moisture transfer. This is a high performance fabric that resists
sweat stains, provides comfort, sun protection and a wonderful ‘soft-hand’
feel (Prabhakar Bhat and Bhonde 2006).
The study carried out by Corinne Keiser et al (2008) showed that
the moisture content of a single layer is not only dependent on the material
properties of that particular layer, but mainly on properties of the neighboring
layers or even of the whole combination. These results suggest that the second
layer of the combination proved to be of high importance for the moisture
distribution. If the second layer is a hydrophilic layer, it absorbs moisture and

57. 64
leads it to the outer layers, while a hydrophobic second layer only takes up
little moisture, and act as a liquid water barrier and the moisture will either be
stored in or drip off.
Behera et al (2002) produced bi-layer interlock knitted structures
using 100% polypropylene and 100% cotton spun yarn and studied for
transmission behaviours of air, water and heat in order to assess their
suitability for sportswear. Wicking coefficients in multilayered fabrics were
much better than in others of 100% cotton. Malgorzata (2006) studied the
thermal insulation properties of multi layer textiles.
2.15 FRICTIONAL PROPERTIES OF FABRICS
As a fabric is moving across the skin, displacement of skin is
increased and the perception of fabric roughness or smoothness is evoked.
The friction and mechanical interaction between fabric and skin during
contact are the key factors determining the perception of roughness,
smoothness and scratchiness. It has been identified that roughness and
scratchiness are important tactile sensations determining the comfort
performance of next-to-skin wear. The friction between skin and fabric is
smaller in fabrics with a smooth surface than fabrics with rougher surfaces.
Moisture at the skin surface can alter the intensity of perceived fabric
roughness. As moisture content increases, the friction and displacement of
skin increases, which triggers more touch receptors. Therefore, a fabric that is
perceived to be comfortable at low humidity conditions may be perceived to
be uncomfortable at higher humidity or sweating conditions.
Behmann (1990) reported a study on the perception of roughness
and textile construction parameters. The roughness was defined as
irregularities in the surface, which can be described geometrically by the size
of the rough elements, or mechanically by the friction coefficients. In 2002,
Okur found that the frictional resistance of the fabrics knitted with carded

58. 65
yarns was higher than that of fabrics knitted with combed yarns. Protruding
fibers on the fabric surface were the most important factor affecting fabric
surface smoothness and frictional properties. Polyester fiber has higher
coefficient of friction as compared to viscose.
Apurba Das et al (2005), examined the fabric-to-metal surface and
fabric-to-fabric frictional characteristics (in both warp and weft directions) of
a series of fabrics containing 100% polyester, 100% viscose, and P/C & P/V
blends with different blend proportions. In P/C and P/V blended fabrics, the
frictional force increases as the cellulose fiber component increases, and the
blended fabrics show higher fabric-to-fabric friction than 100% polyester or
100% viscose. P/C blended fabrics show higher frictional force than that of
P/V blended fabrics for the same geometrical parameters of the fabrics.
Apurba Das et al (2007) analyzed the frictional characteristics of
woven suiting and shirting fabrics with different blends, construction
parameters and found that the fabric to metal friction is less sensitive to fabric
morphology and rub direction, whereas the fabric to fabric friction is highly
sensitive to the type of fiber, blend, yarn structure, fabric structure, crimp,
compression etc. For all fabrics kinetic friction is always lower than static
friction of different levels.
Marek Snycerski et al (2004) designed a double-layer woven fabric
with different friction coefficients on the right and left sides of the fabric, and
differential frictional coefficient along warp and weft direction. Mário Lima et
al (2009), described novel patented laboratory equipment, which was studied,
designed, and manufactured at the University of Minho, Portugal, based on a
new method of accessing frictional coefficient of fabrics. The authors
compared fabrics produced with a new generation of fibers, namely polylatic
acid (PLA) fiber and soya protein fiber (SPF) and confirmed that SPF is softer
than PLA.

59. 66
2.16 TEXTILE BASED ELECTRONIC DEVICES FOR
COMMUNICATION
The integration of microelectronic devices in textiles can be very
useful for communication and controlling aims, especially for occupational
clothing and medical applications. These smart textiles have already gained a
foothold in professional clothing (for fire, police and rescue services) where
sensors and information technologies are merged into uniforms for the benefit
of the wearer with increased ease of use as a result (Tao 2005; Tao 2002;
Friedrich 2006).
In recent years, electro textiles have emerged as a promising
material for body-worn wireless systems, which allows the smart clothes to
communicate freely through wireless network. Since electro textiles are
usually light weight, durable and flexible, they are considered as a suitable
material for wearable antennas in body-worn wireless systems (Sigurd
Wagner 2002; Ashok Kumar 2007; Salonen 1999; 2001). A lot of research
has been carried out on various materials for the construction of wearable
antennas which are designed to be an integral part of clothing. By
implementing conductive fibers, either as such as metal plated textile fibers or
thin metal wires, any textile structure, including knitted, woven or nonwoven
textiles, can be made electrically conductive (Yuehui Ouyang et al 2005;
Justin et al 2006).
Sabine Gimpel et al (2004) prepared a partially conductive textile
structure as basic substrate to integrate sensors and microelectronic devices
into textiles. The proceeding is based on two steps. The first is to create a
textile pre structure by conventional textile technologies, such as jacquard
weaving, embroidery etc. using silver-coated polyamide threads. The second
is a galvanic and/or electrochemical treatment of the textile pre structure.
Carla Hertleer et al (2008) carried out a research on the feasibility of using
textile materials for antenna design by combining nonconductive textiles for
substrate and conductive electro textiles for antenna patch and ground plane.