Cooling fabric blocks heat from pavement and buildings in hot cities

Future city dwellers could beat the heat with clothes made of a new fabric that keeps them cool.

The textile, made of a plastic material and silver nanowires, is designed to stay cool in urban settings by taking advantage of a principle known as radiative cooling – the natural process by which objects radiate heat into space.

The material selectively emits infrared radiation within the narrow band of wavelengths that can escape Earth’s atmosphere. At the same time, it blocks the sun’s radiation and infrared radiation emitted by surrounding structures.

Po-Chun Hsu at the University of Chicago in Illinois and his team designed this material to “try to block more than half of [the radiation] from the buildings and the ground”, he says.

Some cooling fabrics and building materials already rely on this radiative cooling principle, but most of those designs do not account for radiation from the sun or infrared radiation from structures like buildings and pavement. They also assume the material would be oriented horizontally to the sky like panels on a rooftop, rather than the vertical orientation of material in clothes worn by a person.

Those designs work well “when you are facing a cooler object such as the sky or an open field”, says Hsu. “However, that’s rarely the case when you are facing an urban heat island.”

Hsu and his colleagues designed a three-layer textile. The inner layer is made of a common clothing fabric like wool or cotton, and the middle layer consists of silver nanowires that reflect most radiation.

The top layer is made of a plastic material called polymethylpentene, which doesn’t absorb or reflect most wavelengths, but emits a narrow band of infrared radiation.

In outdoor tests, the textile stayed 8.9°C (16°F) cooler than a regular silk fabric and 2.3°C (4.1°F) cooler than a material that emitted radiation across a broad range. When tested on skin, the textile was 1.8°C (3.2°F) cooler than a cotton fabric.

Hsu says this small difference in temperature could theoretically increase the time someone could comfortably be exposed to heat by up to a third, although this hasn’t yet been tested.

“Making this stuff practical as a textile is always difficult,” says Aaswath Raman at the University of California, Los Angeles, adding the work is a good demonstration of translating the physical principle of radiative cooling to a usable material. Other materials with similar properties could also be used on the vertical surfaces of buildings, he says.

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