A textile knit with carbon nanotube–coated fibers trap or dissipate heat according to how hot and sweaty the wearer is. Most people deal with temperature changes in their surroundings with a sartorial strategy: for example, short sleeves for a balmy day outside and a sweater for the air-conditioned office. A new smart fabric could help regulate body heat and eliminate the need for multiple layers of clothing. The textile, knit from carbon nanotube–coated triacetate-cellulose fibers, cools wearers down or warms them up depending on how hot and sweaty their skin is.
Two effects give the fabric its thermostat-like properties, says YuHuang Wang, who, along with Min Ouyang, led the team at the University of Maryland, College Park, that developed the textile. First, the carbon nanotubes act like a metal, Wang explains, effectively transforming the fibers into tiny antennas. Depending on the spacing between the fibers, these antennas interact differently with infrared radiation emitted from a person’s body. This IR radiation accounts for more than 40% of the heat exchanged between our bodies and the environment.
Heat and humidity dictate the distance between the fibers because their hydrophilic cellulose and hydrophobic triacetate components respond differently to moisture. When they’re in a hot and wet environment, the fibers move closer together, and this spacing lets IR radiation escape. When the environment is cold and dry, the fibers move apart and trap IR radiation. Wang likens the smart fabric to a room with blinds, which can be adjusted to let light in or out. Regular fabric is like a room without windows or doors, he says. There’s no way for the light to escape.
The distance between fibers also affects the spacing between strands of yarn that the fibers are spun into to make the textile, leading to its second temperature-regulating mechanism. When it’s hot and the fibers move closer together, the strands of yarn in the fabric pull away from one another, allowing body heat to escape. When it’s cold, the fibers move away from one another, causing the yarn strands to move closer together and trap heat within the garment (Science 2019, DOI: 10.1126/science.aau1217).
The textile not only has applications for helping manage body heat, “but it also is important for fabricating smart and functional fabrics,” says Zhong Lin Wang, a smart materials expert at the Georgia Institute of Technology.
YuHuang Wang says the fabric feels like cotton, and it can be washed and dyed without changing its properties. He acknowledges that there are safety concerns with wearing fabric coated in nanotubes, but the group is working to address that problem. While there are military and health-care applications for the fabric, Wang predicts it will first show up in sportswear; Under Armour is already testing it, he says.