The cross-sectional shape of a fiber has a significant effect on the thermal insulation characteristics of fabrics [504,514]. A fiber’s cross-section with more trapped dead air may provide better thermal insulation. For example, a hollow fiber traps more dead air inside its structure than a commonly available solid circular fiber (Fig. 7.3). This is the reason that a hollow cotton fiber-based fabric can provide better thermal insulation than a solid circular synthetic fiber-based fabric . In the same fashion, a noncircular or profiled fiber (trilobal, scalloped oval) traps more dead air than a circular fiber because a noncircular fiber has more loops on its surface than a circular fiber. This greater amount of trapped dead air ultimately enhances the thermal insulation characteristics of the fabrics made from these fibers [506,507]. The latest development in the market is a hollow nanofiber, such as a carbon nano tube that can be used in protective clothing [20,21].
Fig. 7.3 Fiber cross section with trapped dead air.