2. WHAT DOES SHOWERPROOF MEAN?
Showerproof fabric is fabric that resists
water. We could pour a glass of water over it
and watch the liquid simply form beads and
run off.
But shower proof fabric allows water vapour
to pass through it.
Thus it is comfortable to wear.
3. METHOD OF PRODUCING SHOWER PROOF
FABRIC
There are several methods which can be
used to obtain fabrics which are both
breathable and waterproof. These can be
divided into three groups:
• Densely woven fabrics
• Membranes
• Coatings
4. DENSELY WOVEN FABRICS(PORE SIZE 10-31M)
These fabrics are made from
finest types of longest staple
cottons, using low twist
mercerized yarns, woven
using an Oxford weave, which
is a plain weave with two
threads acting together in the
warp.
The fabric weight ranges from
170 to 295 gsm.
5. COTTON
Until quite recently, most waterproofs and tents
were made from special close-woven cotton.
Most cottons for tents and jackets also have
some form of treatment which helps them to
shed water without absorbing too much.
They need re-spraying from time to time with
this.
In general, cottons are comfortable to wear and
hardwearing, but they tend to be heavy,
especially when wet, their waterproof qualities
are limited, they take a long time to dry out and
they are liable to rot.
6. NYLON
Most waterproofs and tents are nowadays made of nylon.
Nylon fabrics are very light and strong, packing away into
a small bundle.
They can be coated in a variety of ways to render them
either totally waterproof or breathable-waterproof.
Nylon doesn't absorb much water and so takes very much
less time to dry out than cotton.
It is also resistant to rot. All in all, nylon is more practical
for fieldwork.
The problem for manufacturers with nylon fabrics is that
they deteriorate when exposed to sunlight, and are
weakened when coated with the various waterproofing
treatments
7. MEMBRANES
Membranes are
extremely thin films
made from polymeric
material and engineered
in such way that they
have a very high
resistance to liquid
water penetration, yet
allow the passage of
water vapour.
A typical membrane is
only about 10 μm
8. DIFFERENT TYPES OF MEMBRANES
1. Microporous membrane (pore size 3-0.11 μm)
This if thin film expanded
polytetrafluoroethylene (PTFE)
polymer claimed to contain 1.4
billion tiny holes per square
centimeter.
These holes are much smaller
than the smallest raindrops (2-3
μm compared with 100 μm ),
yet very much larger than a
water vapour molecule (40-10^-
6 μm ).
9. DIFFERENT TYPES OF MEMBRANES
2.Hydrophilic membrane (pore size below 0.001μm)
Hydrophilic membranes are very
thin films of chemically modified
polyester or polyurethane
containing no holes.
The polyester or polyurethane
polymer is modified by
incorporating up to 40% by weight
of polyethylene oxide.
The poly ethylene oxide
constitutes the hydrophilic part of
the membrane by forming part of
the amorphous regions of the
polyurethane polymer system.
10. COATING
These consist of a layer of
polymeric applied to one
surface of the fabric.
Polyurethane is used as the
coating material. Like
membranes, the coatings
are of two types,
microporous and
hydrophilic. These coatings
are much thicker than
membrane.
11. MICROPOROUS COATINGS (PORE SIZE 3-2 μ M)
Microporous
coatings have
similar structure to
the microporous
membranes.
12. HYDROPHILIC COATINGS (PORE SIZE BELOW
0.001 μM)
The difference between
micropous material and
hydrophilic material is
that with the former,
water vapour passes
through the permanent
air permeable structure
whereas the later
transmits vapour by
molecular mechanism
involving adsorption-
diffusion and desorption
