New Fabric Releases Heat When You Sweat

New Fabric Releases Heat When You Sweat

Materials scientists at Duke University create tiny vents that trap thermal energy when it’s dry, but let the heat out when a person starts sweating. These holes close to re-hold heat when dry.

Using physics instead of electronics when punching holes, this material can be applied to different types of clothing that will keep the wearer comfortable in a wide variety of situations.

The new approach the researchers developed was presented online three days ago in the journal Sciences Advances.

Po-Chun Hsu, an assistant professor of mechanical engineering and materials scientist at Duke University, explains: “People who ski or walk in cold weather often wear clothing in layers, so they can control how much heat their clothing traps as their bodies warm up. But by strategically placing a material that can dissipate heat when a person sweats, we can create a fabric for any occasion.”

When Hsu attempted to make such a material that could be used in both ways, he turned to nylon. Nylon is a cheap, light and soft material. Hsu also knew that if cut into fins, the nylon curls a little when one side is exposed to moisture.

But nylon is not very suitable for making warm clothing. That’s why Hsu added a layer of heat-trapping silver to the top. Thinking that the weight of the silver would block the nylon fins, Hsu tried to make the layer as thin as possible. But he was surprised to find that the silver he added actually caused the fins to curl much more.

Experimenting with silver of various thicknesses, Hsu discovered that the optimal point was around 50 nanometers; that is 2,000 times thinner than a sheet of paper. The thinner it is, the weaker the effect is. When it was thicker, the weight of the silver began to interfere with the drilling of the holes.

Working with Cate Brinson, professor of mechanical engineering and materials science at Duke University, Hsu discovered something even more interesting.

“It sounds surprising and counterintuitive, but adding something heavy on top of a polymer can actually make it bend and open more,” says Brinson. “As a result, silver shrinks and nylon expands.”

Video: Duke University
Video: Duke University

Brinson and graduate student Boran Ma say that when the substrate gets wet, the nylon wants to expand like a leaf that pulls away from its sides. But because it’s attached to silver at the top, it can’t flex in these directions. The easiest option left is to have the two-layer material crimp, allowing the nylon to expand while the silver contracts.

Author: Ken Kingery/Duke University.


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