The movement of liquid water in clothing, known as wicking, is governed by the attraction between liquid water and the fibre surface, known as surface energy, and the size of the spaces between fibres. Wool has a hydrophobic waxy coating naturally but can be treated to increase its hydrophilicity and wicking. Sportwool fabric is treated with agents to increase the surface energy of wool while maintaining a hydrophobic outer layer, allowing sweat to wick to the outer layer and spread out for evaporation.

1. Wicking of Liquid Water in Wool
The movement of liquid water in clothing, known as wicking, is governed
by quite different physical principles to moisture vapour absorption and
desorption, which are associated with the movement of water vapour
molecules through the internal chemical structure of the fibre.
Wicking only involves the external surface of the and synthetic fibres is shown in the accompanying
fibre. This surface can range from being either table. Most apparel fibres have similar surface
hydrophilic (water loving) if it attracts liquid water to energy, with the notable exception of cellulosic
hydrophobic (water hating) if it is water repellent. fibres such as cotton, linen and flax. The high
surface energy of cellulosic fibres is the reason they
There are millions of tiny interconnected airspaces are used widely for water absorbing products such as
between the fibres that make up textile fabrics. The bath and tea-towels. It is relatively easy to modify
parallel alignment of fibres in yarns and the small wicking behaviour by increasing or decreasing fibre
physical dimensions of the spaces between them surface energy. Active sportswear fabrics, such as
mean that fabric wicking behaviour is governed by SportwoolTM, are commonly treated with hydrophilic
similar principles to the wicking of liquids in agents to increase their surface energy and hence
capillaries. The key drivers in this process are the increase wicking performance (see graph 1). At the
attraction between the liquid and the fibre surface other end of the spectrum, hydrophobic polymers
(known as the fibre surface energy) and the physical such as silicones and fluorocarbons are used to
size of the capillaries themselves. reduce the surface energy of fabrics to stop wicking
altogether for end-uses such as rainwear.
The surface energy of a number of generic natural
Fabric
Skin Moisture vapour

2. Fibre Surface energy
(mJm2)
rate of moisture build-up
Aramid -30 100% synthetic
Carbon 40 -50
Cellulose 200
Polyacrylonitrile 44 sweating starts
Polyamide 46
Polyester 43
Polyethylene ~22 sportwool
Polypropylene 29
0 2 4 6 8
Polyvinylchloride 37
minutes of exercise
Wool 29
Table 1: The surface energy of natural and synthetic Graph 1: Increased wicking performance of
fibres SportwoolTM .
In its natural state, the outer surface of the wool manufacture with a hydrophilic agent that slightly
fibre is covered with a layer of lipids or waxy increases the surface energy of the wool but
materials that are relatively hydrophobic. Wool substantially increases the surface energy of the
fabrics manufactured from fibres that have not been outer polyester face. This difference in surface
chemically treated do not tend to wick water or only energy is what drives the one-way wicking behaviour
do so quite poorly. Some traditional wool products of Sportwool as shown in Figure 1.
used before modern surface treatments were
available involved coating the fabric with a natural Wicking is also a key factor in the drying of fabrics. It
grease to keep water out. This was a trick used on is a popular misconception that synthetic fabrics dry
their wool gloves by Scandinavian fishermen. If the more quickly than their natural counterparts. In fact
lipids are removed by processes such as chlorination the rate of evaporation from fabrics depends solely
or oxidised by plasma treatment the fibre surface on the prevailing climate conditions and is quite
becomes quite hydrophilic. Wool fabrics treated in independent of the fibres involved. Drying time is
this way wick water quite well. Machine-wash treated determined by the amount of water in the fabric that
wool fabrics often wick noticeably better than their must be evaporated. After a wash and spin-dry cycle
untreated equivalents. The wool used on the inner fabrics that wick strongly retain more water and take
face of Sportwool for example is machine-wash longer to dry than poorly wicking fabrics.
treated. Sportwool fabrics are treated after
Figure 1: The wicking behaviour of SportwoolTM.
1. During vigorous 2. Sweat is picked up 3. The moisture is then 4. There it spreads out
activity, the body from the skin by the rapidly pulled through to increase the area of
produces sweat. inner wool layer of the to the outer layer. evaporation.
Sportwool TM fabric.