Polar bears have translucent fur that appears white because of the way light bounces around the structure of the hair itself. The long, coarse guard hairs, which protect the plush thick undercoat, are hollow and transparent. The thinner hairs of the undercoat are not hollow, but they, like the guard hairs, are colorless. Polar bear fur will absorb much of the UV light that strikes it, and with an astonishing 95% efficiency, their white fur is capable of converting solar radiation into heat, which gives the bears some much-needed warmth. Beneath all that thick fur, polar bears have jet black skin.