When winter winds chill us to the bone, we bundle up in sweaters, down vests and fleece parkas. Wild animals, on the other hand, must endure the cold. A mammal’s fur and its thick layers of fat provide insulation that conserves body heat. Fur is made of two kinds of hair: guard hairs and underfur. Guard hairs are long and glossy and lay over the shorter, duller, downier underfur. Guard hairs waterproof the animal’s coat by blocking moisture and keeping the underfur dry. They also protect the