Wool, the hairlike covering on the bodies of sheep, is one of the important textile fibers in use today. Wool is soft, warm, and flexible. It can be woven, knitted, and felted into hundreds of different textiles, from thin veiling to thick, nubby tweeds.
Wool is obtained from more than 200 different breeds and crossbreeds of sheep throughout the world. The breed of the sheep influences the type and grade of the wool produced. The quality and nature of wool are also decided by the climate in which the sheep are bred, by the food that the animals eat, and by the age and general health of the sheep. The finest wool is generally produced by the Merino sheep. The Merinos originated in Spain but are now bred in many other countries. The very coarse wools used for carpets and rugs are obtained mainly from the breeds of Asian countries and New Zealand.
The hair of some other hoofed animals— such as the Angora and the Kashmir goat, camel, alpaca, llama, and vicuña—is also often classified as wool. But strictly speaking, the hair of these animals is not wool, since it does not have the same structure.
Like hair, wool grows out of the skin. And like hair, wool has a horny outer layer. But in hair this layer is smooth. In true wool fiber, it consists of rows of overlapping scales, much like fish scales or shingles on a roof. When wool fibers are twisted or pressed together tightly, the scales lock into one another, especially when wet. This property makes wool a most desirable fiber for felting. It is also the reason that wool materials are easily matted when they are washed and squeezed.
Wool fibers vary in length from 4 to 35 centimeters (1% to 14 inches) and may be thinner than human hair. As a rule, the finer the fiber, the more highly prized it is. Each single wool fiber is bent in curls, or crimps. When a fiber is stretched and then released, the crimps pull it back into its original position. This is one of the factors that give wool fabrics their great elasticity (springiness). Wool is the only fiber that behaves this way naturally. The crimps also keep air trapped between the fibers. Air is a good insulator and does not let warmth escape from the wearer's body.
