fiber made from the fleece of the domestic sheep.
Wool consists of the cortex, overlapping scales (sharper and more protruding than those of hair) that may expand at their free edges causing fibers to intermesh; elasticum, the inner layer; and a core. When soaked, the elasticum and core contract, shrinking the fiber. Elasticity resulting from the molecular structure of wool and resiliency from its crimp make wool fabrics crease resistant. Fine wool will stretch one third its length. Wool is warm because its fibers are nonconductors of heat and its crimp permits it to enmesh still air. It is highly absorbent and releases moisture slowly. Its tensile strength is one fourth greater than that of cotton. A protein compound of complex chemical composition, it is soluble in hot caustic soda.
Wool is classed as follows: fine, usually short-staple wool of Merino fineness and including Delaine Merino, combable fibers 2 in. (5.1 cm) or more in length; medium, or mutton, 2 1/2 to 6 in. (6.4–15.2 cm) long, e.g., Cheviot and Southdown; long-staple, 10 to 15 in. (25.4–38.1 cm) long, loosely crimped, e.g., the Lincoln and the Cotswold; and carpet, 1 to 15 in. (2.5–38.1 cm) long, strong, coarse, and usually blended for uniformity. For industrial purposes the fiber of the camel, Angora goat (see mohair), Kashmir goat (cashmere or pashmina), llama, alpaca, and vicuña is classed as wool.
Sheep are sheared with mechanical clippers. The fleece thus recovered is classed as lamb's wool, or first clip; hog wool, clipped from sheep 12 to 14 months old; wether wool, from older animals; taglocks, the ragged, discolored portion; and pulled wool, usually weakened when recovered by sweating or chemical processes from sheep slaughtered for mutton.
The wool is sorted as to fineness, crimp, length of fiber, and felting qualities. Dirt, suint (dried perspiration), and lanolin are removed by a soap-alkali scouring; by the expensive naphtha solvent method, which retains the full strength and softness of the fiber; or by freezing and shaking. Wool may be carbonized to remove vegetable matter. It is bleached and dyed as raw stock, yarn, or in the piece; it is oiled to withstand processing and is often blended.
Woolen goods are woven from carded short-staple fibers into soft yarns adapted to fulling and napping. Worsted fabrics such as whipcord, gabardine, and serge have a hard, smooth texture. Originally made only from long-staple fibers, worsted yarn is now spun also from medium or short fibers. The fibers are carded, the resulting sliver gilled to straighten the fibers and double them for uniformity; subjected to successive combings to remove nails (short ends) and lay the fibers parallel; then drawn into roving and spun, usually by the rapid, continuous ring method, and twisted. Although the twill weave is usual for worsteds, the same weaves may be used as for woolens without the pattern being obscured by the napping, fulling, and shearing processes commonly employed in finishing woolens.
No known wild sheep are wool bearing. The supposed ancestors of the domestic sheep had long hair and a soft, downy undercoat, which under domestication gradually became wool, while the long hair disappeared. In this development, breeding, feed, climate, and protection were influential, as shown by an atavistic return of neglected sheep to long hair and rudimentary wool.
In the tombs and ruins of Egypt, Nineveh, and Babylon, in the barrows of early Britons, and among the relics of the Peruvians, fragments of woolen fabrics are found. The Romans as early as 200 B.C. began to improve their flocks, which became the progenitors of the famed Spanish Merino sheep. The Britons kept sheep and wove wool long before the Roman invasion, but the establishment by the Romans of a factory at Winchester probably improved their methods. William the Conqueror brought into England skilled Flemish weavers. Henry II encouraged wool industries by laws, cloth fairs, and guilds of weavers. Edward III brought weavers, dyers, and fullers from Flanders. England became the great wool-producing country of Europe, and wool was the staple of its industry until cotton began to overshadow it in the 18th cent.
In the American colonies, sheep raising started in Jamestown. Stringent English laws against exporting wool passed in an attempt to force the use of English cloth on the colonies, early drove the settlers to the raising of sheep. George Washington imported sheep and brought spinners and weavers from England. Early in the 19th cent., imported Merinos greatly improved the existing stock. Spinning and weaving were early established in New England, at first in homes, later in small factories. The first factory in America using water power to weave wool was established (1788) at Hartford, Conn., and was encouraged by tax exemption and a bounty on each yard woven.
In the United States, by the Wool Products Labeling Act of 1939, the term wool may be applied only to fabrics made entirely of new wool; the term reprocessed wool, to wool recovered from unused articles and waste; and reused wool, to wool reclaimed from used articles. The trade designates fleece wool as virgin wool, salvaged wool as shoddy. Salvaged wool may legitimately be used to add strength to soft new wool or to produce a cheaper product. Numerous synthetic fibers have been developed as wool imitations and for blending with wool.
The United States now produces a substantial amount of the world's wool, chiefly in Texas, Montana, Wyoming, Utah, Oregon, Idaho, New Mexico, Colorado, California, and Ohio. Woolen cloth manufacture is largely centered in New England. Other important wool producers include Australia, Argentina, New Zealand, Russia, the Republic of South Africa, Uruguay, Great Britain, China, and India.