The thick fur insulates the body of the polar bear against the extreme cold of its arctic environment but polar bears actually have transparent, hollow hair called guard hair. These clear colored air filled guard hair help transmit heat from the sunlight to their black skin as a solar heat collector. Their guard hair are waterproof, so they also help keep the bear warmer when it is in water. Reflection of the sunlight from the transparent hair makes polar bears appear white, in the same way as reflection of the sunlight makes snow and ice look white. The dense fur completely hides the black skin underneath, which absorbs the heat energy from sunlight; plenty of light still passes through the transparent hair.