Polar bear fur isn't white, it's clear

Shave a polar bear and you won't find pale skin. You will find a creature that is jet black from its nose to its tail. This dark pigment is a survival heater designed to soak up every possible scrap of solar radiation in the Arctic.

Even the fur isn't actually white. Each strand is a clear, hollow tube that functions like a fiber optic cable. These tubes scatter and reflect visible light, which makes the bear appear white to our eyes, but their primary job is to funnel ultraviolet heat directly down to that black skin.

Because the skin is so efficient at absorbing heat, polar bears struggle more with overheating than with freezing. They regularly take swims in ice water just to cool their core temperature down. If they run for too long, their own insulation can become a death trap.

Interestingly, because they are so perfectly insulated, polar bears are almost invisible to infrared cameras. They radiate so little heat into the air that they blend perfectly into the frozen background, leaving only their warm breath and black noses visible to thermal sensors.