Researchers have created a fabric that automatically regulates the amount of heat that passes through, depending on conditions; for example, when conditions are warm and moist — such as those of a sweating body on a summer day — the fabric allows infrared radiation (radiant heat) to pass through. When conditions become cooler and drier, the fabric reduces the heat that escapes. Infrared radiation is a primary way the body releases heat and is the focus of this new technology.
The fabric was created from specially engineered yarn coated with a conductive metal. In 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. This action is referred to as “gating” of infrared radiation, which acts as a tunable blind to transmit or block heat.
The base yarn for the new textile is created with fibers made of two different synthetic materials — one absorbs water and the other repels it. The strands are coated with carbon nanotubes. Because materials in the fibers both resist and absorb water, the fibers warp when exposed to humidity such as that surrounding a sweating body. That distortion brings the strands of yarn closer together, which does two things. First, it opens the pores in the fabric. This has a small cooling effect because it allows heat to escape. Second, it modifies the electromagnetic coupling between the carbon nanotubes in the coating.
This coupling effect is like bending a radio antenna to change the wavelength or frequency it resonates with. Imagine bringing two antennae close together to regulate the kind of electromagnetic wave they pick up. When the fibers 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.
Depending on the tuning, the fabric either blocks infrared radiation or allows it to pass through. The reaction is almost instant, so before people realize 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 technique enables switching of both the porosity and infrared transparency of a textile so as to provide increased comfort in response to environmental conditions. More work is needed before the fabric can be commercialized. Materials used for the base fiber are readily available and the carbon coating can be easily added during standard dying process.