Fat acts as a nutritional reserve and energy storage when food can’t be found, and may provide the ability to generate heat to help insulate polar bears from the freezing air and cold water. This fat may also help the bears float in the water. It is 2 to 4 inches (5 to 10 centimeters) thick. Find out more!

Unlike brown bears and black bears, polar bears do not hibernate, and only pregnant females over-winter in dens. While in the den, the pregnant female’s activity level decreases and her metabolism slows down.

During this period, she gives birth and nurses her cubs. Sometimes, when weather conditions are particularly rough, other bears may dig temporary shelters, where they spend several days at a time.

When not hunting, polar bears are resting, perhaps as much as 20 hours a day. Polar bears are great bed makers, building nest-like beds in seaweed piled up on the coast, digging deep caves of snow into the bluffs, or resting in a shallow snow bed and letting the blowing snow cover them, making for a snug day den.

A pregnant female stays in a snow den throughout her pregnancy, the birth of her cubs, and the first few months of the cubs’ life, without leaving the den. Changes in her metabolism allow her to go without food, water, defecation, or urination for as long as eight months.