The term is usually used for the fleece of sheep, but according to the Textile Fiber Products Identification Act, wool is defined for purposes of labeling as: “The fiber from the fleece of the sheep or lamb or hair of the Angora or Cashmere goat (and may include the so-called specialty fibers from the hair of the camel, alpaca, llama, and vicuna) which has never been reclaimed from any woven or felted wool product.”

Wool is used in a variety of blends in which it is combined with nearly all natural or manufactured fibers. Wool fibers have scales that tend to interlock with each other, binding the fibers together. This process is called felting. In blends, particularly those with manufactured fibers, wool is used to improve the feel or appearance of finished products. Manufactured fibers are sometimes blended with wool to enable the spinning of very fine or loosely twisted yarns with increased tensile strength or to produce ease-of-care properties. Wool can be treated to control shrinkage, to provide resistance to damage by moths, to impart stain-resistance, and to set permanent creases in fabrics.