Perhaps no other animal symbolizes the frozen tundra regions of the Earth more than polar bears. They live on ice and snow, but an outer coat of long guard hairs that stick together when wet protects a dense, thick undercoat of fur that keeps them warm. Even though polar bears look white, their hair is really made of clear, hollow tubes filled with air, providing extra insulation. A thick layer of fat, two to four inches, acts as a nutritional and energy reserve when food is scarce, helps produce body heat, and also helps the bears float in the water. Polar bears spend their days hunting and sleeping after a good meal, usually seals. When not hunting, polar bears are resting, as much as 20 hours a day.