Wool and silk are two common animal fibers. Wool is obtained from the fleece of sheep, goats, camels, yaks, llamas and alpacas. These animals have thick coats of hair or fleece that insulate their bodies from heat and cold. Sheep wool is most commonly used. Silk is obtained from the cocoons of silkworms. Silkworms are caterpillars that eat mulberry leaves and spin cocoons made of silk fibers to pupate. The cocoons are processed to reel out the silk fibers, which are then spun into thread and woven into silk fabric.