Clothes and covers made of a smart fabric that radiates heat and reflects light could help people and objects that are out in the sun stay several degrees cooler.
Guangming Tao at Huazhong University of Science and Technology in Wuhan, China, and his colleagues developed what they call a “metafabric” by combining microscopic beads and fibres of titanium oxide, Teflon and a plastic called polylactic acid embedded within larger fibres.
The beads of titanium oxide – also found in sunscreens – and Teflon reflect ultraviolet and visible light, while the polylactic acid fibres emit infrared light. The sizes of the particles are designed to optimise these properties.
“Through structural control, our metafabric achieves a nearly perfect mid-infrared emissivity, thereby maximising heat dissipation,” says Tao.
In one test, a volunteer wearing a vest made half of the metafabric and half of cotton sat in direct sunlight for an hour. The skin temperature under the metafabric rose from around 31°C to 32°C over that time, while the temperature under the cotton rose to around 37°C.
In another test, one car was covered with the metafabric, another with a shop-bought cover and a third was left uncovered. When left in the sun from 11am to 1pm, the temperature rose to 60°C in the uncovered car, 57°C in the car with the standard cover and 30°C in the one with the metafabric cover over that period.
The metafabric is most effective when in contact with the skin. If someone wore a garment made of the metafabric over a thick layer of normal clothing, much of the cooling effect would be lost because less body heat would be conducted to the metafabric and then radiated away.
The researchers are focusing on cooling people and objects exposed to direct sunlight, but there would still be a cooling effect in the shade, says Tao. The fabric could be dyed different colours, but white is the most effective for reflecting sunlight.
“This technology can be seamlessly connected with mature, modern manufacturing,” says Tao. Some well-known clothing brands are interested in the metafabric, he says. “We hope that our products will be available in a year or so.”
“This work is absolutely impressive based on its outdoor cooling performance,” says Po-Chun Hsu at Duke University in North Carolina.
Hsu and his colleagues have developed cooling fabrics that work in a different way. Instead of emitting infrared, they are transparent to it. One of the main ways that our bodies lose heat is by emitting infrared from our skin, but normal clothing blocks most infrared radiation.
This team has shown that wearing infrared-transparent clothes indoors is equivalent to reducing the temperature by 2°C. Hsu thinks the widespread adoption of such clothing could help tackle climate change by reducing the demand for air conditioning.
Journal reference: Science, DOI: 10.1126/science.abi5484
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