A polar bear looks like the whitest animal on Earth, a snowdrift with legs. So it comes as a small shock to learn that the bear under all that fur is not white at all. Peel back the coat and the skin is jet black, and the fur itself was never really white to begin with. The bear is hiding two surprises at once, and both of them are about surviving the cold.

A polar bear's skin is black to soak up heat

A polar bear's skin is black so it can absorb as much warmth from the sun as possible in one of the harshest climates on the planet (Polar Bears International). Dark surfaces are good at swallowing light and turning it into heat, the same reason a black car bakes in a parking lot while a white one stays cooler. For an animal that spends its life on sea ice, every spare degree of warmth is worth holding onto.

The black comes from melanin, the same pigment that colors human skin and hair. Polar bears carry a heavy dose of it, and that load may do double duty. Beyond catching heat, the dark pigment likely shields the skin against ultraviolet radiation bouncing off the snow, which can be fierce in the Arctic. Tellingly, no albino polar bear has ever been recorded in the wild or in a zoo, a strong hint that black skin matters too much to do without.

The fur is not white either

Here is the second twist, and it is the stranger of the two. A polar bear's fur is not white. Each hair is pigment-free and transparent, with a mostly hollow, air-filled core (Polar Bears International). There is no white dye anywhere in the coat. The bear only looks white because of what those clear hairs do to light.

When sunlight strikes the coat, it bounces around inside and between thousands of clear, hollow strands. The light scatters and reflects in every direction, and that even, colorless scatter is what your eye reads as white (San Diego Zoo Wildlife Alliance). It is the very same trick that makes a snowbank look white even though a single ice crystal is clear, which is also exactly why snow is white. Crush a pane of glass into powder and the heap turns white for the same reason. The polar bear, in effect, wears a coat of shattered light.

That clear coat also explains why polar bears are rarely a clean snow-white. The hollow hairs pick up tints from the world around them. Oils from a seal-fat meal can leave the coat cream or yellow, dirt can smudge it brown, and captive bears in warm, damp zoos sometimes go faintly green when algae grows inside the hollow hairs. The color you see is a property of the light and whatever clings to the fur, not of the fur itself, in much the same way that veins look blue without actually being blue.

The myth of the solar bear

For a long time, a tidy story tied all this together. The hollow, clear hairs, people said, worked like fiber-optic cables, piping sunlight and ultraviolet light straight down to the black skin to be turned into heat. It sounded perfect. A natural solar collector growing on a bear. The claim spread through newspapers, books, and classrooms for decades.

Then someone tested it. Daniel Koon, a physicist at St. Lawrence University, measured how much light actually traveled along a polar bear hair and found the answer was almost none: less than a thousandth of a percent of red light, and a far tinier fraction of violet, made it even an inch down a shaft. Far from guiding light to the skin, the keratin in the hair mostly absorbs it. Scientists still agree the black skin helps catch warmth, but the hairs are not light pipes funneling the sun down to it. The fiber-optic story was a tidy explanation that happened to be wrong.

A coat built for the cold

Strip away the myth and what remains is still impressive. The bear pairs a clear, hollow, double-layered coat (coarse guard hairs over a soft woolly undercoat) with black skin underneath, and the whole arrangement is tuned to trap warmth where almost nothing else can. The fur insulates so well that polar bears barely lose any heat, which becomes a real problem in summer when they can overheat. The black skin and clear coat are survival gear, the same kind of climate adaptation you see in why camels carry humps at the opposite extreme.

So the next time you see a polar bear glowing white against the ice, remember you are not really looking at its color at all. You are seeing clear hair throwing sunlight back at you, the way the sky scatters blue, which is its own story in why the sky is blue. The real bear underneath has jet-black skin, soaking up what little warmth the Arctic sun can spare.

Keep wondering: find out why snow is white when a single ice crystal is clear, learn how camels survive their own brutal climate, and discover just how cold space gets.