Fabric

Skin Moisture vapour

Wicking of Liquid Water in Wool

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 TMmean that fabric wicking behaviour is governed by Sportwool , 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

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.

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

Aramid

Carbon

Cellulose

Polyacrylonitrile

Polyamide

Polyester

Polyethylene

Polypropylene

Polyvinylchloride

Wool

-30

40 -50

200

44

46

43

~22

29

37

29

Fibre Surface energy2(mJm )

0 2 4 6 8

sweating starts

100% synthetic

sportwool

minutes of exercise

rate

of

mo

istu

re b

uild

-up

1. During vigorousactivity, the bodyproduces sweat.

2. Sweat is picked upfrom the skin by theinner wool layer of the

TMSportwool fabric.

3. The moisture is thenrapidly pulled throughto the outer layer.

4. There it spreads outto increase the area ofevaporation.

Graph 1: Increased wicking performance of TM Sportwool .

Table 1: The surface energy of natural and synthetic fibres

TMFigure 1: The wicking behaviour of Sportwool .