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A material that radiates or traps body heat as it is stretched or released could lead to smart apparel whose warmth wearers could adjust to stay comfortable during exercise or when the weather changes (APL Bioeng. 2024, DOI: 10.1063/5.0169558).
Think of the material as an adaptable, comfortable version of the foil blankets that keep marathoners and people in disaster zones warm by reflecting and trapping body heat. “It is as breathable as cotton, washable, and can be integrated into any fabric,” says Alon Gorodetsky, a chemical and biomolecular engineering professor at the University of California, Irvine.
Gorodetsky and colleagues were inspired by the color-changing ability of squid. The cephalopods rapidly expand or contract pigment-loaded sacs in their skin, and this changes the wavelength of light their skin reflects and transmits. Instead of reflecting visible light, the researchers’ material reflects varying levels of infrared heat radiation.
The researchers coated a rubbery styrene-ethylene-butylene-styrene (SEBS) polymer sheet with a superthin film of copper. During manufacture, the copper film cracks into small islands. When the polymer is relaxed, the islands stay together, and the copper film reflects heat. But the islands move apart as the polymer is stretched, allowing heat to pass through.
The researchers covered the film with another SEBS layer to make it water resistant. They used a laser to perforate the material with an array of pinpoint holes of just the right size and location so the material retains its strength while allowing air and water vapor through. Finally, they attached the material to a commercial mesh fabric using standard adhesives. The composite can withstand at least 20 wash cycles.
The researchers imagine using clips or buttons to control how much the material is stretched and hence how much heat it traps. But a more automated way to actuate the material will be key for practicality, says Lucy E. Dunne, an expert on wearable technology and apparel design at the University of Minnesota Twin Cities. “That’s not impossible in e-textiles. We have many examples of shape-changing textiles using approaches like shape-memory alloy fibers, but it’s a significant challenge.”
Different levels of stretching the material regulate temperature over an 8 °C range. But adjusting the temperature can require stretching by up to 50%, which might make use in clothes tricky, says Jyotirmoy Mandal, who researches thermoregulating materials at Princeton University. The technology might be better suited for use in buildings or other structures, he says. The material’s robustness and “use of relatively common materials ensure scalability and low-enough cost needed for real-life use,” he says.
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