Polar bears are warm–blooded mammals, yet they live in freezing Arctic temperatures. They retain their body heat because of a thick coat of fur as well as a thick layer of fat under their skin. Fur and fat are poor conductors of heat, or good insulators.

A polar bear's fur is the first step in keeping warm. Polar bears actually have two types of fur: long oily guard hairs and short insulating hairs. Polar bears stay warm by combining the properties of these two hairs. The guard hairs are actually hollow. These hollow guard hairs trap warmth and bring it close to the skin to help polar bears stay warm while also providing an oily outer layer which prevents the polar bear from getting wet. The insulating hairs help polar bears stay warm by trapping heat close to the skin. Under their fur, polar bears have black skin which is good for absorbing the rays of the arctic sun.