As record-high temperatures rack the globe, rethinking how we stay cool is increasingly important. Energy-hungry air-conditioning is already contributing to global warming, and its use will only go up as the world warms.

Cooling individuals instead of entire living spaces consumes less energy. So researchers have designed a new wearable fabric to help people beat the heat in urban settings. The material, reported in the journal Science, could find use in clothing, cooling facades for buildings and cars, and for food storage and transport.

In sweltering temperatures, cities become heat islands because pavements, roads and densely packed buildings absorb and retain heat.

Existing cooling fabrics reflect sunlight and also wick away sweat to cool a person via evaporation. More recently, researchers have designed cooling fabrics that rely on the principle of radiative cooling: the natural phenomenon in which objects radiate heat through the atmosphere straight into outer space.

But radiative cooling fabrics made so far are designed to work when laid horizontally as opposed to vertically, as they would be when worn. Plus, their effectiveness diminishes in urban heat island settings. That’s because in addition to getting heated by the sun from above, the fabrics absorb heat that the ground and nearby buildings radiate.

For urban cooling, researchers at the University of Chicago made a new three-layer fabric. Its wool bottom layer wicks heat from the skin to the middle layer, which is made of silver nanowires that block heat from coming in. The top layer selectively emits heat into the atmosphere.

To make the fabric, the researchers had to carefully engineer and tune the materials to respond differently to visible sunlight and thermal radiation. “You need to have a material that has two optical properties at the same time. That’s very challenging to do,” said Chenxi Sui, a PhD student in molecular engineering at the University of Chicago.

In tests conducted in the urban heat island of Chicago and under blistering Arizona sun, the material stayed 2.3°C cooler than sports cooling fabrics and 8.9°C cooler than commercial silk used for summer clothing.

Source: Ronghui Wu et al. Spectrally engineered textile for radiative cooling against urban heat islands. Science, 2024.