Wool is an animal fiber that forms the fleece, or protective coat, of sheep. Coarser than most vegetable or synthetic fibers, wool fibers are wavy (up to 10 waves per centimeter) and vary in color from the usual white to brown or black. They are composed of the protein keratin, whose molecules are long, coiled chains, giving wool elasticity and resilience. Reactive side groups result in good affinity for dyes, and enable new, desirable properties to be chemically imparted.
Wool lasts if well cared for, but is liable to be damaged by some insect larvae (which eat it), by heat, sunlight, alkalis, and hot water. It chars and smolders when burned, but is not inflammable. Wool strongly absorbs moisture from the air. It is weakened when wet, and liable to form felt if mechanically agitated in water.
Wool has been used from earliest times to make cloth. Sheep are shorn, usually annually, and the fleeces are cleaned – the wool wax removed is the source of lanolin – and sorted, blended, carded (which disentangles the fibers and removes any foreign bodies), and combed if necessary to remove shorter fibers. A rope of woolen fibers, roving, is thus produced and is spun (see spinning). The woolen yarn is woven into cloth, knitted, or made into carpets or blankets.