How do animals protect themselves against cold?

Penguins have a thick plumage and a thick layer of fat. In addition, their body shape-a lot of mass with the smallest possible surface-ensures that the animals lose very little of their body heat. Polar bears protect themselves with the help of a layer of fat, but they also have another heating mechanism. Individual hairs of their fur are hollow and conduct the little sunlight available to the skin like glass fibre cables. Their skin is black-not bright like other animals-and black stores heat. Since the undercoat of the polar bear's hide is very thick, body heat is not lost; therefore, the polar bear is able to survive even the freezing cold of the Arctic.