Ice doesn't stick to polar bear fur - but why?

In the frozen expanse of the Arctic, polar bears glide effortlessly across ice and plunge into sub-zero waters – yet their fur is remarkably free of frost.

For years, scientists have wondered: How do these apex predators avoid turning into walking ice cubes? The answer, it turns out, is as simple as it is surprising: greasy hair.

Researchers analyzed hair samples from six wild polar bears. They discovered that the fur’s sebum, made of cholesterol, diacylglycerols, and fatty acids, plays a crucial role in preventing ice buildup.

When the grease was removed, the fur lost its ice-resistant properties and behaved similarly to human hair, which allows ice to adhere easily.

The research offers new insights into how polar bears adapt to their harsh environment. It also opens up possibilities for developing new materials that resist ice accumulation.

Polar bears’ greasy fur

The study was led by Julian Carolan, a PhD candidate in the School of Chemistry at Trinity College Dublin and the AMBER Research Ireland Centre.

“We measured ice adhesion strength, which is a useful measure of how well ice sticks to fur; hydrophobicity, which dictates whether water can be shed before it freezes; and freezing delay time, which simply shows how long it takes for a drop of water to freeze at certain temperatures on a given surface,” explained Carolan.

“We then compared the performance of the polar bear hair with that of human hair and two types of specialist human-made ‘ski skins.'”

The results confirmed that greasy, unwashed polar bear hair strongly resists ice. When washed, the fur lost its grease and performed similarly to human hair, to which ice sticks easily.

Further chemical analysis revealed a surprising detail – polar bear sebum does not contain squalene. This fatty compound is common in human hair and in aquatic mammals like sea otters. Its absence in polar bears suggests a key evolutionary adaptation that helps them resist ice accumulation.

Nature-inspired innovation

Dr. Richard Hobbs highlighted the broader impact of this discovery. “Animals living in polar habitats have emerged as a source of inspiration for the development of new anti-icing materials,” he said.

“For example, Anne Kietzig’s group at McGill University recently found that the hierarchical structure of Gentoo penguin feathers afforded them anti-icing properties that relied on the feather structure rather than the preen oil coating.”

“Our work shows that polar bear fur provides an alternative strategy to produce an anti-icing surface based on the characteristic blend of lipids present in their fur sebum or hair grease.”

This study not only clarifies why polar bears avoid ice buildup but also suggests new ways to create sustainable, ice-resistant coatings. Researchers hope to replace environmentally harmful chemicals like PFAS, commonly used in current anti-icing coatings, with alternatives inspired by nature.

Unique properties of polar bear fur

Beyond its scientific applications, this discovery provides valuable insights into polar bear hunting techniques and Inuit traditions.

Professor Bodil Holst from the University of Bergen explained how this adaptation benefits polar bears in the wild.

“One of the polar bears’ main hunting strategies is ‘still hunting,’ where they lay motionless beside a breathing hole on sea ice waiting for seals to surface. Still hunting frequently develops into an ‘aquatic stalk’ with the polar bear using its hind paws to slide into the water to pursue its prey, and the lower the ice adhesion, the less noise generated and the faster and quieter the slide.”

Inuit hunters have long understood this advantage. They sometimes cover their hunting stools with polar bear fur to reduce noise while moving on ice. Additionally, polar bear trousers (made using the same principle) allow hunters to move quietly without alerting prey.

Importantly, traditional Inuit preparation methods preserve the natural grease in the fur. Unlike fox fur, which is often cleaned with soapstone or dry clay, polar bear fur is kept unwashed to maintain its unique properties.

Implications for future technology

This research not only deepens our understanding of Arctic survival but also has practical implications for future technology.

By studying how nature prevents ice buildup, scientists aim to create more sustainable solutions for industries that require ice-resistant materials.

Polar bear fur, with its naturally occurring grease, may inspire the next generation of eco-friendly coatings that could be used in transportation, winter sports, and industrial applications.

The study is published in the journal Science Advances.

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