Jacket that gets thinner when you sweat could help avoid overheating
A material made from bacterial cellulose alters its insulating properties in dry and moist conditions, which could help you stay a comfortable temperature whatever the weather
By Alex Wilkins
13 August 2025
The jacket is thicker when dry (left) and thinner when moist (right)
Xiaofeng Jiang/Nanjing University of Aeronautics and Astronautics 2023
If you find yourself endlessly taking your jacket on and off when the sun disappears behind clouds, a material that becomes thinner when you sweat could provide a solution.
Researchers have previously developed self-adapting materials that can cool you down in hot climates by increasing the amount of heat, in the form of infrared radiation, that the material lets through. But these materials tend to work in only one direction and are poor at keeping people warm in cooler climates.
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Xiuqiang Li at Nanjing University of Aeronautics and Astronautics in China and his colleagues have developed a jacket that contains a layer that curves up when dry and flattens when wet. This makes the jacket get thicker in cooler environments and thinner in warm ones, triggered by a person’s sweat. “Sweat production offers a more straightforward and timely indicator of the body’s actual heat-dissipation needs,” says Li.
The clothing has a similar design to regular down jackets, but contains a layer of cellulose produced by bacteria, which is then reinforced with polyester to make it strong enough to expand an outer layer of fabric. Li and his colleagues found that the cellulose layer, which becomes predictably more curved as it dries, can remain fixed in place at one angle for 12 hours, and still works after 200 cycles of changing from flat to curved.
The team tested how much heat the material kept in while on top of cloth with varying levels of moisture. They found it to be as cool as a polyester shirt when wet and almost as warm as a down jacket when dry.
