Fiber properties

Fiber properties have a significant impact on the thermal insulation characteristics of fabric. These fiber properties are fineness, cross section, length, and crimp [169,170,259,504,506,507].

Fineness or linear density

Normally, more fine fibers can fit in a certain volume than coarse fibers because the diameter of a fine fiber is less than a coarse fiber (Fig. 7.2); this implies that a greater fiber surface to volume ratio is obtained in the case of fine fibers. As fiber surfaces trap dead air (boundary air layer), it is obvious that the fine fibers will trap more dead air than the coarse fibers. Consequently, fine fiber-based fabrics possess better thermal insulation characteristics than coarse fiber-based fabrics [2,504,508,509]. In this regard, the latest development in the commercial market is superfine nanofibers, whose diameter varies between 50 and 500 nm and can greatly enhance thermal

Fig. 7.2 Number of fine and coarse fibers in a certain volume.

insulation. These nanofibers cannot be produced by conventional melt or wet spinning methods; therefore, a new electro-spinning method is widely applied to manufacture nanofibers [510-513].