The sea otter is one of the smallest marine mammal species and unlike other marine mammals has no blubber and relies on its fur to keep warm. With nearly one million hairs per sq in, its fur is the most dense of any animal. The fur consists of long waterproof guard hairs which keep the dense underfur layer dry. In this manner, cold water is kept completely away from the skin and heat loss is limited. The ability of the guard hairs to repel water depends on cleanliness. Due to its loose skin and unusually pliable skeleton, the sea otter has the ability to reach and groom the fur on any part of its body. In adults, the color of the head, throat, and chest are lighter in color than the rest of the body leading to the appearance of a grey whiskered old man.