Early humans chose skins, furs and feathers to stay warm. Wool and cotton fabrics followed. All these materials keep us warm by trapping a layer of air next to our skin. They also reflect infrared radiation, back towards the body. This is the heat given off by a person even when they are perfectly still. To create a fabric which actually cools the skin has been a challenge. Now scientists at Stanford University have created a fabric that will keep wearers cooler than anything except wearing nothing at all. The team, lead by Yi Cui, have modified polyethylene (a common plastic) which is used as a cling film for food.
Polyethylene contains atom arrangements that allow infrared radiation to pass through. To make it more suitable for clothing, Cui and his team wanted to retain polyethylene’s transparency to heat but without the see-through qualities. They discovered that the material already exists – nano-porous polyethylene. It’s a type of polyethylene used in the battery industry. The holes in nano-porous polyethylene are 100 times smaller than that of human hair. This means the holes are a similar size to the wavelength of visible light. The result is the scattering of light, making the plastic no longer transparent to human eyes.
The material is bright white in appearance. Plastic film does not usually have wicking properties but the scientists punched additional larger holes, about the size of a human hair, in the material. This allows air to permeate and perspiration to evaporate. Then by adding a polydopamine coating, they enhanced the fabrics wicking. The final stage was to encapsulate a layer of cotton mesh between two layers of the plastic. In tests the new material was 2.7º cooler than cotton when worn. This small figure is significant as lowering a static persons temperature by just a few degrees can save up to 45% of energy used to power a building’s air conditioning system.