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Imagine running around outside in a heavy down jacket. Even if it’s cold out, you might start to feel too warm. And much like you in that jacket, a polar bear is so well insulated that it can easily become overheated by moving too fast. “It will often grab a mouthful of snow to cool off,” says polar bear biologist François Messier. “Or it may lie flat with its legs extended to expose its belly directly to the snow, since belly fur is much less dense.” To keep from overheating, a polar bear usually moves slowly and doesn’t run very often.
 So what keeps the polar bear so toasty in the Arctic deep freeze? The most visible protection is its thick fur coat. The coat has two layers: an outer layer of long, dense guard hairs and an undercoat of short woolly hairs. The guard hairs are actually hollow tubes that direct the sun’s rays to the bear’s skin. A polar bear may look white, but underneath its hair its skin is black. Dark skin absorbs more heat than light skin.
Another way a polar bear copes with the cold is with built-in insulation: a layer of blubber under its skin that can be more than four inches thick. The bear’s blubber and thick fur pull double duty, keeping it warm in icy water as well as on land.
“People tend to view the Arctic as a harsh environment,” says Messier. “But if you have a species with the correct adaptations, then it’s not necessarily a harsh environment for them.”
 A polar bear spends the winter living on sea ice—ice formed when the ocean freezes. But the bear has no trouble keeping its footing on slippery ground. Its paws are perfect for getting around on a slick, cold surface. Rough pads give it a nonslip grip, and thick fur between the pads keeps the bear’s feet warm. It uses the sharp, curved claws on its front paws like hooks to climb onto the ice from the water. Polar bears’ claws also help them dig in the ice when they hunt seals.
Some polar bears—pregnant females—spend the winter hibernating. They dig a den in the fall, give birth inside in early winter, and stay there until spring. With a big, warm polar bear inside it, the den’s temperature can be 40 degrees (4°C) higher than the outside.
Though other polar bears don’t hibernate, there are stormy times when wind and blowing snow make travel and hunting too difficult. “So they just curl up and let the snow cover them,” says Messier. “It’s warmer under the snow than it is being exposed to the air.”
So bring on the snow, wind, and icy water. Because when it comes to keeping warm, a polar bear’s got it covered!
For more about polar bears, check out Creature Feature: Polar Bears.
Photographs at upper right and center by Paul Nicklen
Photograph at lower left by Flip Nicklin
Text by Kathy Kranking
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