At some point, your mom may have said, “If you're cold, put on a sweater!” Or if you were hot, she might've said, “Why are you wearing those skinny jeans? No wonder you're roasting!” Usually, warming up is an additive process, while cooling off is subtractive.
But there's only so much clothing you can remove before the authorities show up or you get a serious sunburn. Fortunately, researchers at Stanford University have developed a textile that lets body heat (infrared radiation) escape without letting visible light in, making it one of the coolest fabrics ever invented.
“Regular textile materials like cotton aren't transparent to the infrared radiation our bodies put off,” says Dr. Yi Cui, a professor of materials science and engineering at Stanford who worked on the fabric. “We invented a nanoporous polyethylene fabric that's transparent to infrared radiation but is opaque to visible light, because the nanoporous structure scatters it. At the same time, the porous structure allows for air to move around and perspiration to come out.” In short, the fabric that makes you feel like you're naked in the shade.
The fabric, which is based on a material used in the manufacture of lithium-ion batteries, has pores that are only 50 to 1,000 nanometers across — large enough to allow the escape of both water vapor and the wavelength of radiation bodies naturally release, but small enough to scatter visible light. Although the fabric is made of polyethylene, the same plastic used to make milk jugs, plastic bags and athletic wear, the difference between it and store-bought running tights is considerable. They both let infrared radiation and sweat escape, but normal polyethylene fabric reflects only about 20 percent of visible light. The nanoporous polyethylene (nanoPE) reflects 99 percent of the visible light spectrum, making it opaque.
Sure, this material would probably make great workout clothes. But the goal of this research is loftier: to tackle climate change and unbridled energy consumption, two of the most pressing environmental problems of the 21st century. Because much of the way we keep cool or warm these days involves piping cold or hot air into a room, regulating the temperature of indoor spaces is currently a chief concern among residential energy hogs — about 48 percent of the energy consumed in the U.S. homes is for heating and cooling. Regulating individual body temperature would save a lot of the energy used to cool an entire building, Cui says.
So how much cooler would a person feel wearing nanoPE rather than cotton? According to the research team, the fabric would keep you 4 degrees Fahrenheit (2 degrees Celsius) cooler than cotton. That may not seem so impressive, but the team estimates the collective result of everyone setting the thermostat just a few degrees higher in the summer could yield up to 45 percent energy savings. Plus, the researchers are working on making the fabric durable and comfortable to wear, as well as developing dyes that don't block the infrared radiation from escaping.
And that might just be worth the new wardrobe.