You might imagine a polar bear dripping with ice after a long swim, but that’s not really what happens. Polar bears definitely get wet when they hunt or cross icy water, but they come out mostly ice-free thanks to special oils in their fur and the thick fat beneath their skin.
A polar bear’s fur resists freezing even after a dunk, so they stay mobile and ready to hunt.
Let’s dig into how their fur and body fat work together, why their hair structure matters, and what scientists have found about the grease that keeps ice from sticking to their coat. There’s some fascinating science here about how polar bears deal with water and cold.
How Polar Bears Get Wet and Stay Warm
Polar bears swim in freezing water, using thick fat and layered fur to keep warm. They shed water quickly so they don’t stay cold for long.
Swimming and Arctic Waters
You can picture polar bears diving for seals in icy seas. They swim long distances—sometimes tens of kilometers—to reach sea ice or hunt.
Their paws paddle and their bodies float, thanks to a thick layer of fat. Cold water chills their skin fast, but polar bears rely on speed and good swimming technique.
They push through waves, then climb out onto ice or snow to stop losing heat. Scientists discovered that oils on their fur help repel water, so it doesn’t stick and freeze on the hair surface (see this Science Advances reporting at NPR).
Role of Body Fat and Fur Layers
You might reach for a jacket to trap heat; polar bears do the same with fat and fur. Their blubber can be several centimeters thick and acts as the main insulator during swims.
Fat keeps their core organs warm, even when the outer fur gets wet. Their fur has two layers: dense underfur and long guard hairs.
The underfur traps air for extra insulation. The guard hairs are oily and hollow, which helps reflect light and shed water.
This combo keeps warmth close to their skin and slows down heat loss during and after a swim.
Drying After a Swim
When you get out of cold water, you dry off to avoid getting chilled. Polar bears do something similar—they shake, roll in snow, and groom themselves to remove water from their fur.
That quick drying keeps ice from forming on the coat and brings back the insulating air layer. Sebum oil on their skin makes water bead up and run off, so their fur dries faster than you’d expect.
Hunters in Arctic communities have long used polar bear fur for water-shedding clothing because of these traits.
The Science Behind Water and Ice Resistance
Polar bear fur stays dry and ice-free because oily secretions on the hairs change how water and ice stick. Specialized lipids help fur repel water and reduce ice adhesion, while missing certain oils keeps sticky frost from building up.
Polar Bear Hair Grease and Sebum
Sebum comes from glands under the skin, coating each hair with a thin oily layer. On polar bears, this grease spreads over both the hollow guard hairs and the dense underfur.
That coating slows water from soaking in and helps droplets bead and roll off. The grease also changes the hair’s surface energy, so water can’t grip the hair as easily.
When you touch wet fur, it feels oily rather than soaked because the oil sits between the water and the hair shaft. Inuit people have used polar bear hide for ice-resistant clothing for this very reason.
Compounds Involved: Diacylglycerols and Cholesterol
Researchers found that the grease contains lots of diacylglycerols and cholesterol. Diacylglycerols act like short, oily molecules that create a slippery film on the hair.
Cholesterol makes the film more rigid and helps it stick to fur in cold, wet conditions. These compounds are naturally hydrophobic, so they repel water.
That lowers ice nucleation, making it harder for ice to bond to the hair. Together, diacylglycerols and cholesterol give the coating both slipperiness and stability, even in freezing temperatures.
Absence of Squalene and Its Impact
Unlike some other mammals, polar bear sebum doesn’t have squalene—a common oily molecule in many animal skins. Squalene can get sticky or oxidize, which sometimes encourages ice crystals to stick.
By not using squalene, polar bears avoid that sticky problem on their fur. Without squalene, their grease stays less viscous and less likely to form hard residues.
That keeps the fur slippery at low temperatures and lowers the chance that thin ice will stick to the hairs and build up into heavy, insulating crusts.
Anti-Icing Properties and Natural Deicing
The mixed lipid film on polar bear fur makes ice stick less, so when ice starts to form, it just falls off with a little movement. If a bear shakes, walks, or even takes a swim, those frozen bits usually slide right off instead of clinging stubbornly to the fur.
The oil layer does something else, too—it limits how many places ice can start forming. That means less ice shows up in the first place.
Researchers actually checked how much ice sticks to polar bear hairs, and the results were about the same as those fancy anti-icing surfaces people engineer in labs. That’s pretty wild, right? Looking into these lipids might help us come up with better coatings for things like aircraft, power lines, or wind turbines.
Honestly, you could call polar bear fur a natural, self-renewing deicing system. Nature’s got some clever tricks up its sleeve.
