Natural fibers may be of animal, vegetable, or mineral origin. Although the annual production of vegetable fibers outweighs that of animal or mineral fibers, all have long been useful to humans.

Animal fibers

Animal hair fibers consist of a protein known as keratin. It has a composition similar to human hair. Keratin proteins are actually quite similar to the synthetic fiber nylon, where the repeating units are amino acids. The fibrous proteins form crystals. They also crosslink through disulfide bonds present in the cystine amino acid.

Silks are partially crystalline protein fibers.

Wool forms the protective covering of sheep, screening them from heat and cold, and allowing them to maintain even body temperatures. The following are important characteristics of wool fibers. (1) They are 1-14 in (2.54-35.56 cm) or more in length, with diameters of 0.0016-0.0003 in (0.04 - 0.008 mm). (2) Their average chemical compositions are: carbon, 50%; hydrogen, 7%; oxygen...