Seals, whales and walruses all happily splash about in chilly ocean waters—kept warm by a thick layer of blubber. Sea otters, though just as happy zipping through could waters, are relatively svelte in comparison. The reason? Their magnificent fur coats. The thick fuzz is roughly 1,000 times more dense than human hair and can trap air bubbles, which insulate the otters in frigid water.
But no one had ever looked deeply into the fur's mechanics, until now. A team of researchers at MIT recently examined the properties of otter and beaver fur, with hopes of unlocking its fuzzy secrets. Their results, published in the journal Physical Review Fluids, could serve as a guide to new bioinspired materials, including warm, furry wetsuits.
“We are particularly interested in wetsuits for surfing, where the athlete moves frequently between air and water environments,” Anette (Peko) Hosoi, senior author of the study and mechanical engineering researcher at MIT, says in a press release. “We can control the length, spacing and arrangement of hairs, which allows us to design textures to match certain dive speeds and maximize the wetsuit's dry region.”
Hosoi says the project was inspired by a visit she made to Taiwan with a group of students. They visited a sporting goods manufacturer that made wetsuits and the company asked if the students had any ideas for sustainable or biologically inspired materials or tweaks to make better suits. Back home, Hosoi tasked graduate student Alice Nasto with brainstorming solutions. Nasto realized the fur of semi-aquatic mammals might have some relevance to the problem, but no one had yet delved into the mechanics of their pelts.
The researchers found that longer guard hairs trap water droplets, preventing them from slipping into the pelt to the shorter underfur, which holds air pockets that insulate the otter’s skin, reports Weston Williams for The Christian Science Monitor. To test the idea, they fabricated fur-like surfaces with thousands of soft rubber hairs, mimicking otter or beaver fur. They then mounted the hairy surfaces to a motorized stage and submerged them in silicone oil to examine how the density of the hairs impacted the formation of air pockets. It turned out that the denser the hair and the faster the material was submerged, the more air was trapped. The team was able to express those relationships as an equation, according to the press release.
The findings could revolutionize wetsuit design. “Currently, wetsuits are made of heavy neoprene rubber materials,” Nasto tells Williams. “Interestingly, air is 10 times more insulating than neoprene rubber. So if you could make a suit from a textile that traps the same thickness of air as the thickness of a typical rubber suit, it would be ten times as insulating and also more lightweight.”
But this research could have much broader applications. The equation describing this relationship could be useful for manufacturing processes such as industrial dip-coating, helping researchers calculate how long to dip an object before it starts to trap air.
It’s not completely obvious how the hairs could be applied to a wetsuit, but the researchers are thinking about it. “Of course, you could make a very hairy wetsuit that looks like Cookie Monster and it would probably trap air,” Hosoi says in the press release. “But that's probably not the best way to go about it.”