The opposite effect occurs in cool conditions, when the textile is cold or dry: the fibers expand, reducing gaps to prevent heat from escaping.
In cooler, drier conditions, the fabric traps more infrared heat, resulting in the wearer staying warmer.
The base yarn is developed using fiber which is made of two different synthetic materials.
The fabric is made of specially engineered yarn coated with a conductive metal. Because these changes are triggered by the conditions in which the fabric resides, the user automatically benefits from the temperature regulation without having to do anything. The strands are coated with carbon nanotubes, which is a special lightweight, carbon-based, conductive metal.
The human body absorbs and sheds much of its heat in the form of infrared radiation.
That distortion brings the strands of yarn closer together, which opens the pores in the fabric.
"You can think of this coupling effect like the bending of a radio antenna to change the wavelength or frequency it resonates with", said Professor YuHuang Wang, also from the University of Maryland. Under hot, humid conditions, the strands of yarn compact and activate the coating, which changes the way the fabric interacts with infrared radiation to allows more heat. "But this fabric is a true bidirectional regulator", said UMD professor and paper coauthor Min Ouyang. When the fibers are brought closer together, the radiation they interact with changes.
Depending on the tuning of the nanotubes, infrared radiation is either blocked or allowed to pass through - and this happens nearly instantly. The reaction is nearly instant, so before individuals realize they're getting hot, the garment could as of now be cooling them down. As the body cools down (and is less sweaty or humid), the dynamic thermal gating mechanism works in reverse to trap heat.
This pioneering work provides an exciting new switchable characteristic for comfort-adjusting clothing, said Ray Baughman, a professor of chemistry at the University of Texas who was not involved in the study. "Textiles were known that increase porosity in response to sweat or increasing temperature, as well as textiles that transmit the infrared radiation associated with body temperatures".
More work is required before the fabric can be commercialized, however as indicated by the analysts, materials utilized for the base fiber are promptly accessible and the carbon coating can be effectively included amid standard dying process.