New technology for temperature management in outer garments

Prof. Hsu's new body temperature management technology is based on a nylon and silver fabric with vents.

01.24.2022.- A team led by Prof. Po-Chun Hsu, from the Department of Mechanical Engineering and Materials Science at Duke University, has created a lightweight material for temperature management. It traps heat energy when dry and opens tiny vents to let heat escape when a person starts to sweat. Once dry, the vents close again to retain heat.

The material, which uses physics rather than electronics to open the vents, can be used in various types of clothing to help keep the wearer comfortable in a wide range of situations. The method is mentioned in a recent issue of the journal Science Advances.

People who ski or hike in cold weather often wear layers so they can adjust the amount of heat their clothing traps as their body warms, Po-Chun Hsu explains, but strategically placing patches of a material that can letting out heat when a person is sweating, you could imagine making a one-piece textile that works for everything.

When he first tried to make a dual-use material, Hsu turned to nylon. Cut into flaps, it curls back on itself when one side is exposed to moisture. However, since it is not a particularly warm material, Hsu added a layer of silver, which traps heat. Since the weight of silver can mar nylon flaps, he tried to make the layer as thin as possible. To his surprise, the addition of silver made the lapels curve even more.

A combination of nylon and silver

After experimenting with various thicknesses of silver, Hsu discovered a balance point around 50 nanometers, 2,000 times thinner than a sheet of paper. If it were finer, the phenomenon would not be as strong. If it were thicker, the weight of the silver would start to interfere with the opening of the vents.

Baffled by what was happening, Hsu enlisted the help of Cate Brinson, the university's chair of mechanical engineering. She and Boran Ma, a graduate student, found that when the bottom layer of nylon gets wet, it expands like a sheet stretched from the sides. Since it's attached to the silver at the top, it can't stretch in that direction. The easiest option left is for the two-layer material to curl up, allowing the nylon to expand while forcing the silver to shrink.

The researchers then created a piece the size of a hand with flaps of a few millimeters. It is 16% warmer when dry with the lapels closed than a traditional polyester/elastane fabric; and 14% cooler when wet with flaps open. Together, the hybrid of nylon and silver can extend the thermal comfort zone by 30%.

According to Hsu, this approach has advantages over existing methods of venting heat through outerwear.

Now Hsu is working on making the vents as small as possible without losing efficiency. She is also studying the possibility of using a nanocomposite topcoat that could make the material any color without changing its thermal attributes.

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