Stanford scientists are working on a new material which allows significantly more heat to escape from the body than existing clothing fabrics. The report was included in the September 2nd issue of Science, from Stanford materials scientist Yi Cui. Wicking fabrics and wearable fans more or less represent the current cutting edge of cooling clothing devices, both of which take advantage of evaporation to cool the wearer. The new, plastic cling-wrap fabric instead uses nano-sized pores to help release heat as infrared radiation. Traditional fabrics naturally hold this heat in, so allowing it to pass through a fabric could pave the way for a new level of cooling fabrics.
Traditional opaque fabrics block visible light, and in doing so, hold infrared radiation close to the wearer’s body. The challenge was to find an opaque material that also allowed this radiation to escape, which Cui was able to find in a commercially available plastic currently used in lithium-ion batteries. Nanoporous polyethylene, or nanoPE, resembles plastic cling wrap, except that it blocks visible light – it is not clear. Tiny, nano-sized pores distributed throughout the fabric block visible light by forcing blue light and other colors to scatter. According to Cui, the light “bounces around in different directions and scrambles together,” resulting in a white appearance for the fabric. The pores vary in diameter from 50 to 1,000 nanometers, while visible light wavelengths vary from 400 to 700 nanometers. However, infrared light escaping from the body has a considerably larger wavelength: 7,000 to 14,000 nanometers. The pores block the motion of smaller waves, but are like speedbumps for the larger waves which pass through easily.
Tests were done using a hot plate warmed to human skin temperature, and covered the hot plate with tradition fabrics, followed by nanoPE. Cotton fabric raised the temperature from 33.5 degrees Celsius up to 37. The nanoPE fabric raised the temperature only 0.8 degrees Celsius, up to 34.3.
The Stanford researchers have coated the fabric with a water-wicking substance, punched holes for breathability, and layered the fabric with cotton mesh, all attempting to make nanoPE more wearable than plastic wrap. Currently, they are looking into weaving the fabric so it will feel more like traditional clothing. Cui hopes that within 5 years the fabric will exist as wearable clothing, and that within ten years it will become widespread. The report also notes that breathable fabrics like nanoPE could potentially save energy by reducing the use of air conditioning.