A fiber inspired by polar bears traps heat as well as down feathers do

The Arctic’s extreme cold is no match for a polar bear’s super-insulating fur. Humans could one day benefit from a similar material, thanks to a new fiber that mimics the bears’ porous hairs. A sweater knit from the fiber is about one-fifth the thickness of a down coat but similarly warm, researchers report in the Dec. 22 Science.

Like polar bear hair, the fiber’s core is filled with thousands of pores — tiny pockets of air that help prevent heat loss — and surrounded by a flexible, waterproof sheath. But unlike hair, which is made of keratin, the core is built from a synthetic material called an aerogel.

Aerogels are ultralight, porous gels that are excellent insulators. NASA uses them to insulate rocket parts, and they can withstand extreme heat (SN: 2/14/19). However, aerogels tend to be fragile, hindering their use in textiles.

To create a more robust aerogel, materials scientist Hao Bai and colleagues spun and froze a thread of aerogel made from chitosan, a polymer found in the exoskeletons of shellfish. Freeze-drying the string and coating it in a pliable plastic called thermoplastic polyurethane added strength. The resulting fiber can hold up to 500 grams, about the weight of three billiard balls. And it can be knit, dyed and washed. The fiber’s texture falls between plastic and cotton, says Bai, of Zhejiang University in Hangzhou, China.

“I think it can be a product for [the] general public in the near future, in addition to specialized groups” such as the military or space agencies, Bai says.