Effect of fabric properties on comfort

Starr (2010) states that a thin fabric will not provide as much insulation as a thick fabric, due to the inability of the former to trap air. Fan (2009b) adds that surface hairiness and loose construction of a textile contribute to the entrapment of air, which improves insulation.

The three ways in which water can move through a textile fabric is identified by Starr (2010), as sorption, diffusion and wicking. Sorption consists of the following three processes as identified by Starr (2010); adsorption, where water is taken up and held near, or on, the surface of the textile; absorption, where moisture is distributed throughout and in the textile fabric; and desorption, which consists of the release of the moisture from the textile. In terms of diffusion, the moisture in a textile material will disperse more quickly when the fabric has a low mass, an open weave, or is made from bulky yarns (Mehta and Harnett 1981 and Starr, 2010). The ability of a textile material to wick moisture away from the body will depend on fibre wettability as well as the structure of the yarn and fabric (Starr, 2010). According to Mehta and Harnett (1981), wicking not only depends on the properties of fibres and surface finishes, but also on the capillaries in the fabric which facilitate the wicking process.

In terms of finishes used on textiles, Slater (1991) and Ravandi and Valizadeh (2011) state that both mechanical and chemical finishes could result in changes that affect the comfort of the fabric. Mechanical finishes, such as brushing, could increase the bulk of the fabric and trap more air, which influences physiological comfort, whereas chemical finishes and dyeing will generally mainly determine visual and psychological comfort of a garment in terms of the aesthetic appearance of the garment (Slater, 1991). Additional examples of chemical finishes, include crease resistance, stain resistance, antistatic performance, flame resistance and water

85 resistance, all of which contribute to both psychological and physiological comfort parameters (Slater, 1991). Havenith (1999) stated that coatings and membranes on fabrics could also have an influence on the vapour resistance of the fabric. In the final analysis therefore, it is the ability of the fabric to entrap air, together with its mass and thickness and wetting and wicking ability which will determine its comfort.

Of great importance in this respect, is the fabric bulkiness (compactness) and the surface tension and other relevant properties of its fibres and yarns.

As mentioned previously (see Figure 29), the thickness of a fabric largely determines the thermal insulation of the fabric or garment, there being a linear relationship between these two parameters (Chidambaram et al., 2011, Kothari, 2006 and Mehta, 1984).

In a study, conducted by Tyagi et al. (2004), it was found that the thermal comfort properties of woven polyester-viscose fabrics were influenced by the properties of the fibres as well as by the weave construction. The study established that the twill fabrics had better air permeability, water vapour transmission, wickability, absorbency and thermal insulation than the plain weave fabrics (Tyagi et al., 2004).

Das and Kothari (2012) studied the moisture vapour transmission behaviour of 100% cotton plain weave fabrics, with five different pick densities and two different weft counts. Three different methods were used to test the water vapour permeability of the fabrics, namely the Permetest, the cup method and the MVTR cell method. Although the three methods produced different water vapour permeability values, all three methods gave the same trends, the water vapour permeability decreasing with an increase in fabric cover factor (Das and Kothari, 2012). An increase in fabric cover factor reduced the open spaces in the fabric, which ultimately reduced the diffusivity of the fabrics (Das and Kothari, 2012). In addition, the results indicated that the thinner fabrics had higher water vapour permeability than the thicker fabrics (Das and Kothari, 2012).

Oğlakcioğlu and Marmarali (2007) tested various knitted structures containing either 100% cotton or 100% polyester fibres to determine the factors which affect the thermophysiological comfort of the fabrics. Both the Alambeta and the Permetest

86 were used in the study. According to the results obtained on the Permetest, the water vapour permeability of both the cotton and polyester fabrics showed a decrease in value from single jersey (with the highest value), to 1x1 rib (intermediate value), to interlock (lowest value). From their results, they concluded that the effect of knitted structure on water vapour permeability was statistically significant. It should also be noted, however, that the single jersey fabrics had the lowest fabric thickness, which facilitated the easy transportation of water vapour.

Singh and Nigam (2013) investigated the effect of yarn type (combed, carded, and compact spun yarns), the pick density ranging from 88 to 108 filling yarns per inch for each of the three fabrics, on the comfort related properties of 100% cotton plain weave fabrics. The water vapour permeability was tested using the Permetest. The results of the research indicated that the water vapour permeability decreased when the number of picks (weft density) increased from 88 to 108 for all the fabrics (Singh and Nigam, 2013). This was ascribed to the fact that, when the number of filling yarns increased, the fabric cover factor (i.e. fabric compactness) also increased, which reduced the ability of water vapour to pass through the fabric (Singh and Nigam, 2013).

Senthilkumar et al. (2010) studied the air permeability, water absorbency, thermal resistance and wickability of plain weave fabrics produced from polyester/viscose and polyester/cotton blends, and which varied in fabric thickness. The Permetest was used for testing the thermal resistance of the samples. It was found that the fabric with the highest thermal resistance had the highest fabric thickness and fabric cover factor, which enabled more entrapment of air for insulation (Senthilkumar et al., 2010). Senthilkumar et al. (2010) emphasised, however, that the air permeability of the fabric also affected its thermal resistance. In their case, the fabric with the lowest thickness did not have the lowest thermal resistance, which was ascribed to its higher air permeability.

A study conducted by Boguslawska-Bączek and Hes (2013) to test the water vapour permeability of wet wool fabrics, as well as of blended fabrics, using a Permetest, produced the following results:

87 1. An increase in the mass of a wool fabric resulted in a decrease in the water vapour permeability of the fabric, as well as an increase in its water vapour resistance.

2. An increase in the moisture content of wool or wool/viscose blended fabrics had an adverse effect on the ability of the fabric to transport water vapour.

3. The water vapour permeability of the wet fabrics was quite low.

In a study, conducted by Tyagi et al. (2004), it was found that the thermal comfort properties of woven polyester-viscose fabrics were influenced by the properties of the fibres as well as by the weave construction. Coarse polyester fibres, with a non-round cross section, produced good absorbency and thermal insulation; but, reduced the air-permeability and water vapour transmission of the fabric (Tyagi et al., 2004).

In terms of fabric construction, the study established that the twill fabrics had better air permeability, water vapour transmission, wickability, absorbency and thermal insulation than the plain weave fabrics (Tyagi et al., 2004).