According to the American Society for Testing and Materials (ASTM), a fiber is a unit of matter that has a length of at least 100 times its diameter. If fibers are to be used in textile products, they must have characteristics of fineness, strength, cohesiveness, and flexibility appropriate to the projected end use. Chemically, fibers are composed of long chains of molecules called polymers.
Fibers may be found in nature or manufactured. Fibers may be short and noncontinuous or of indefinite length, long and continuous. Short fibers are called staple fibers, while long, continuous fibers are called filament fibers. All natural fibers except silk are staple fibers. Manufactured fibers and silk can be filament fibers or can be cut into staple lengths.
Humans have used natural fibers since prehistoric times. Fibers are often classified according to their chemical structure. Natural fibers obtained from plants are generally made of cellulose. Others, generally obtained from animal hair, are protein. One mineral fiber, asbestos, is obtained from rock deposits. Asbestos products are no longer manufactured in the United States because the fibers can be carcinogenic if inhaled.
Natural cellulosic fibers are classified as seed hair fibers (cotton and kapok) because they grow on seeds. Bast fibers are obtained from the stems of plants (linen from the flax plant, ramie, jute, hemp, and kenaf). Fibers from plant leaves and other vegetable sources include agave, coir, henequen, sisal, yucca, piña, and sacaton. Many of these fibers, and others that are even more rare, have only limited use for industrial products or for local crafts. Cotton, linen, ramie, and hemp are the cellulosic fibers most often used in apparel. Piña comes from the leaves of the pineapple plant and is used for traditional costumes in some Asian and Pacific areas.
Protein fibers are generally obtained from the hair of animals. Silk, another protein fiber, is extruded by the silkworm and obtained from its cocoon. Widely used animal hair fibers include sheep's wool, cashmere, camel hair, mohair, and alpaca. Other animal hair fibers have more limited use. Eskimo women knit qiviut, the soft, fine underhair of the musk ox, into very expensive accessories and garments, using patterns characteristic of their village. Llama and guanaco, Andean animals that are similar to alpaca, and huarzio and misti, cross-bred llamas and alpacas, produce hair harvested for textiles. Attempts to domesticate the vicuña, a wild Andean ruminant, have had limited success. Most of this very soft and costly fiber comes from animals that have been hunted, and strict limits are placed on the number that can be taken each year. In New Zealand, cross-breeding female cashmere goats and male angora goats has produced "cashgora," but marketing efforts for this fiber have had limited success.
Manufactured fibers (sometimes called man-made fibers) can be either regenerated fibers, those formed from natural materials that are not useable as fibers in their natural form, or synthetic fibers from chemical substances. Most manufactured fibers are formed either by melting or dissolving the polymer in a chemical solution, then forcing this solution through holes in a metal plate, called a spinneret, in order to form long, continuous fibers.
The manufacture of a regenerated fiber begins with such diverse substances as cotton fibers too small to be formed into a yarn, wood chips, corn or milk protein, or seaweed. These materials are subjected to chemical processing that allows them to be dissolved and then reformed into filament fibers. The most widely used regenerated fibers include rayon, lyocell, and acetate.
Synthetic fibers are created (synthesized) from chemical substances. The Federal Trade Commission classifies synthetic and manufactured fibers according to their chemical composition. Manufacturers may also give their fibers trade names. The most widely used synthetic fibers are acrylic and modacrylic, elastomers, nylon, polyolefins, and polyester.
Metallic fibers have been used in fashionable apparel for thousands of years, often to make lavish garments to display status. Thin sheets of metal can be cut into narrow strips or a thin filament of metal can be wound around a central core of another material. Except for gold, metal fibers are likely to tarnish unless provided with a protective coating.
Some high-tech fibers with limited use in apparel are aramid, PBI (Polybenzimidazol), melamine, and sulfar. These are used for protective clothing or gloves. Bicomponent fibers are made from two different polymers, combined in various configurations in order to take advantage of the special characteristics of each fiber.
Fibers are made into textiles by techniques in which the fibers are held together or formed into a yarn and the yarns formed into a fabric by any of a number of techniques.
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