In the Arctic, polar bears are equally at home swimming in the frigid waters or galloping across fields of ice and snow. When they emerge from the water, their fur temperature drops to nearly that of the surrounding well-below-zero-degree air. “But you almost never see them have any problem with ice in their fur,” said John Whiteman, a wildlife biologist at Old Dominion University and a research scientist at Polar Bears International. “It’s something that I had never really thought deeply about: is there something unique about their fur?”
However, this phenomenon caught the attention of researchers across science disciplines. Julian Carolan, a graduate student studying bio-inspired anti-icing surfaces working in chemist Richard Hobbs’ group at Trinity College Dublin, explained that the whole project got started because of a nature documentary. While watching polar bears move between the water and the land, experimental physicist Bodil Holst at the University of Bergen wondered at these animals’ ability to prevent their fur from becoming covered in ice. She reached out to Hobbs, and the two outlined a project that Carolan picked up to investigate the anti-icing properties of polar bear fur.
Polar bears are covered by thick fur over the majority of their bodies. The oils on these hairs aid in preventing ice from building up.
Jon Aars
Applying each group’s research strengths, the team demonstrated that the oils in polar bear fur contained a unique fatty acid profile that lent the hair its ice-resistant properties. The study, published in Science Advances, shed light on how these animals survive the Arctic temperatures and offers potential strategies for developing bio-inspired materials.1
To explore the anti-icing properties of polar bear fur, the team first measured the ice adhesion strength of this animal’s hair. They froze a block of ice with a defined area of contact and calculated the amount of force needed to remove this block from the surface. They compared this fur to man-made ski skins, used by skiers to climb snowy inclines, and human hair, donated by Carolan.
“Doing ice adhesion on the polar bear fur itself was kind of a challenge,” Carolan said. Unlike the ski skins that were made to be smooth, the polar bear fur was an uneven surface, so the team had to modify their normal protocol. “What we ended up doing was flipping it, filling the cuvette with [water], and putting the polar bear fur upside down on top, and then allowing it to freeze, and flipping it back.”
They observed that, unlike Carolan’s hair, polar bear fur resisted ice sticking as well as the synthetic ski skins. These skins were treated with a fluorocarbon compound to promote their ice resistance. Because mammal hair is coated in sebum, which provides a water-resistant coating, the researchers wondered if this oil was responsible for polar bear fur’s unique properties.2
When the researchers repeated these experiments after washing each material with soap to remove the sebum, “We found that the ice adhesion increased dramatically,” Carolan said.
Next, they analyzed the polar bear sebum’s composition to identify which components might be responsible for the oil’s ice resistance. Sebum is comprised of lipids and other hydrophobic and hydrophilic compounds that determine its physical properties. Using multiple analytical chemistry techniques, they found that the sebum was rich in glycerol species, waxes, and cholesterols, but was lacking in hydrocarbons, specifically squalene, a common component of sebum in other mammals.
Using in silico modeling, the team assessed how these molecules interacted with ice molecules. They also investigated this for polyfluoroalkyl substances (PFAS) and squalene as comparisons.
They showed that diacyl glycerol species, cholesterols, and long chain fatty acids resisted adhering to ice comparably to PFAS, whereas squalene exhibited high ice adhesion. “[It was exciting] seeing how well polar bear hair oils did compared to the fluorocarbons, because they're very nasty chemicals,” Carolan said. Although PFAS have many useful properties, these compounds do not decompose in the environment or in animals that eat them, leading to accumulation that becomes toxic.3
Julian Carolan (left) and Richard Hobbs (right) at the Trinity College Dublin worked with collaborators at the Norwegian Polar Institute and the University of Bergen to investigate the anti-icing properties of polar bear fur.
Richard Hobbs
“The most striking thing for me was just how effective the anti-icing property seemed to be,” said Whiteman, who was not involved with the study. He added that the multiple approaches to characterize the sebum compounds were thorough and that the comparisons of the polar bear fur to both human hair and synthetic ski skins was clever.
“It’s certainly interesting to see what they have found,” said Andrew Derocher, a wildlife ecologist at the University of Alberta who was not involved with the study but has worked with some of the authors previously. “It gives us a little bit of insight as to some of the mechanisms and the adaptations [of polar bears].”
However, “It's not clear yet how unique this is to polar bears,” Whiteman said, explaining that a comparison to brown bears, polar bears’ closest relatives, would add more insights to the findings.
Derocher agreed. “[Polar bears] are very different than grizzly bears,” Derocher said. For example, unlike polar bears, which he said remain dry down by their skin when they emerge from water, grizzly bears do not. “They're like a wet dog,” he added. “If grizzly bear hair either doesn't have as much of these oils, or they're constructed differently, that would give us a little bit more insight as what's going on.”
Carolan also thought that comparing polar bear sebum to other bears would be interesting. However, he said that his next project will be to further investigate the ice adhesion-resistant lipids that were identified in this study, applying them to different materials to determine if he can mimic the anti-ice properties of polar bear fur.
While the team showed that polar bears resist icing through this chemical method, other animals, such as penguins, rely upon structural properties of their fur or feathers for ice resistance.4 Carolan is interested in materials that combine both properties to improve anti-icing on surfaces. “Maybe if we can kind of marry the structural with the chemical, we could take the penguin structure [and] introduce some of these polar bear hair oils, we can have something that's better.”
- Carolan J, et al. Anti-icing properties of polar bear fur. Sci Adv. 2025;11(5):eads7321.
- Nikkari T. Comparative chemistry of sebum. J Invest Dermatol. 1974;62(3):257-267.
- Evich MG, et al. Per- and polyfluoroalkyl substances in the environment. Science. 2022;375(6580):eabg9065.
- Wang S, et al. Icephobicity of penguins Spheniscus humboldti and an artificial replica of penguin feather air-infused hierarchical rough structures. J Phys Chem C. 2016;120(29):15923-15929.
