Silk modified to reflect sunlight keeps skin 12.5°C cooler than cotton

A fabric manufactured from engineered silk keeps skin about 12.5°C cooler than cotton clothing and relief from hot weather.

Approximately 15 % of global electricity goes towards keeping us cool. To lessen this energy demand, scientists have already been searching for passive means of cooling us that don’t require electricity.

Jia Zhu at Nanjing University in China and Shanhui Fan at Stanford University and their colleagues were inspired by silk, which feels cool against your skin because it reflects almost all of the sunlight that strikes it – mainly the infrared and visible wavelengths – and also readily radiates heat.

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They were able to engineer silk to block a lot more sunlight – about 95 % – by embedding the fibres with aluminium oxide nanoparticles that reflect the ultraviolet wavelengths of sunlight.

When the researchers bathed this engineered silk in sunlight, they discovered that it stayed 3.5°C cooler compared to the surrounding air because of its ability to reflect most sunlight and radiate heat. It is the first fabric to be developed that stays colder compared to the surrounding air when in sunlight.

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The researchers also discovered that if they draped the engineered silk over a surface made to simulate skin, it kept the skin 8°C cooler under sunlight than natural silk did – and it kept the skin 12.5°C cooler than cotton did. The simulated skin was made of silicone rubber that was wrapped around a heater to mimic body warmth.

In the ultimate part of their experiments, they made a collared long-sleeved shirt from the engineered silk and asked a volunteer to wear it while standing out in sunlight on a 37°C day. Infrared images revealed that the shirt stayed cool. Similar infrared images captured of the volunteer wearing shirts manufactured from natural silk or cotton showed these fabrics warmed up. “Wearing the engineered silk on a hot day under sunlight, one feels much cooler than wearing normal textiles such as for example cotton,” says Zhu.

The engineered silk is comfortable to wear, with good breathability, and may be washed and dried repeatedly without falling apart, says Zhu. It is cost-effective to make and could be produced in higher quantities, he says.

The fabric is mainly designed to keep people cool if they are outdoors and exposed to sun, instead of in indoor settings like homes and office buildings, says Fan.

Journal reference: Nature Nanotechnology , DOI: 10.1038/s41565-021-00987-0

More on these topics:

  • materials
  • nanotechnology
  • skin

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