Researchers described in ACS Applied Materials & Interfaces, have made a strong, comfortable fabric that heats and cools skin, with no energy input. A single garment that can adapt to changing weather conditions, keeping its wearer cool in the heat of midday but warm when an evening storm blows in. It can be worn indoors and outdoors, drastically reducing the need for air conditioning or heat.

Smart textiles that can warm or cool the wearer are nothing new, but typically, the same fabric cannot perform both functions. Usually has drawbacks, such as being bulky, heavy, fragile, expensive and many need an external power source.

Guangming Tao and colleagues wanted to develop a more practical textile for personal thermal management that could overcome all of these limitations.

The researchers freeze-spun silk and chitosan, a material from the hard, outer skeleton of shellfish, into colored fibres with porous microstructures. They filled the pores with polyethylene glycol (PEG), a phase-changing polymer that absorbs and releases thermal energy. Then, they coated the threads with polydimethylsiloxane to keep the liquid PEG from leaking out. The resulting fibres were strong, flexible and water-repellent.

To test the fibers, the researchers wove them into a patch of fabric that they put into a polyester glove. When a person wearing the glove placed their hand in a hot chamber (122 F), the solid PEG absorbed heat from the environment, melting into a liquid and cooling the skin under the patch. Then, when the gloved hand moved to a cold (50 F) chamber, the PEG solidified, releasing heat and warming the skin.

The process for making the fabric is compatible with the existing textile industry and could be scaled up for mass production, the researchers say.