Scientists have created a fabric that can automatically regulate the amount of heat that passes through it, helping a person stay cool or warm depending on the weather conditions.
When conditions are warm and moist, such as those near a sweating body, the fabric allows heat to pass through. When conditions become cooler and drier, the fabric reduces the heat that escapes, researchers said.
The researchers from University of Maryland in the US created the fabric from specially engineered yarn coated with a conductive metal.
This is first textile shown to be able to regulate heat exchange with the environment, according to the study published in the journal Science.
Under hot, humid conditions, the strands of yarn compact and activate the coating, which changes the way the fabric interacts with infrared radiation.
They refer to the action as "gating" of infrared radiation, which acts as a tunable blind to transmit or block heat.
"This is the first technology that allows us to dynamically gate infrared radiation," said YuHuang Wang, a professor at University of Maryland.
The base yarn for this new textile is created with fibres made of two different synthetic materials—one absorbs water and the other repels it.
The strands are coated with carbon nanotubes, a special class of lightweight, carbon-based, conductive metal. Since materials in the fibres both resist and absorb water, the fibres warp when exposed to humidity such as that surrounding a sweating body.
That distortion brings the strands of yarn closer together, which opens the pores in the fabric. This has a small cooling effect because it allows heat to escape.
It also modifies the electromagnetic coupling between the carbon nanotubes in the coating, researchers said.
"You can think of this coupling effect like the bending of a radio antenna to change the wavelength or frequency it resonates with," Wang said.
"It's a very simplified way to think of it, but imagine bringing two antennae close together to regulate the kind of electromagnetic wave they pick up," he said.
"When the fibres are brought closer together, the radiation they interact with changes. In clothing, that means the fabric interacts with the heat radiating from the human body," he added.
Depending on the tuning, the fabric either blocks infrared radiation or allows it to pass through. The reaction is almost instant, so before people realise they're getting hot, the garment could already be cooling them down.
On the flip side, as a body cools down, the dynamic gating mechanism works in reverse to trap in heat.
"The human body is a perfect radiator. It gives off heat quickly," said Min Ouyang, a professor at University of Maryland.
"For all of history, the only way to regulate the radiator has been to take clothes off or put clothes on. But this fabric is a true bidirectional regulator," Ouyang said