Undercoat(redirected from undercoats)
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in most mammals, the lower layer of the hairy covering. Made up of soft, fine, twisted hairs, the undercoat fulfills the primary heat-insulating function of the coat. In some animals, for example, Merino sheep, such fine hairs form the entire hairy covering; in others, such as the musk deer, there is practically no undercoat. Aquatic animals and animals adapted to a cold climate have thick undercoats. In wool-bearing animals the underfleece is more valuable than the outer fleece.