A material inspired by plastic wrap could keep you cooler than anything you've ever worn before – perhaps even cool enough to help kill your dependence on air conditioning. Given this weather, I think the heat-wicking duds are coming just in the nick of time.
This summer has been a real scorcher for those of us on the East Coast, and it's made wearing clothes seem like a real chore. A few weeks ago, I made the mistake of taking the subway while wearing a polyester party dress. The synthetic fabric may have looked great, but its water-repellent nature meant that sweat accumulated against my skin instead of seeping through the dress. Sweat cools the body by evaporating into the surrounding air, so as my dress kept the liquid trapped against my skin, I started to look a little too hot. If I'd deigned to wear cotton to a wedding with a dress code of "cocktail chic," I'd have been much cooler — those fibers allow water to escape into the air.
In recent years, new synthetic materials have been designed to wick away moisture even more effectively than natural fibers such as cotton. By actively drawing moisture away from the skin and into the air, these weaves speed the cooling process of evaporation. But they only actually keep you cooler than natural fabrics once you start to sweat, which is why you don't find much formal wear made of the stuff.
A new material described in Science takes that a step further. The fabric doesn't just pull heat away from the body in the form of sweat but also in the form of infrared radiation. Your skin emits this invisible light constantly, radiating heat into the air. That's why you get so toasty when you bundle up under a blanket — you're trapping the heat your skin emits in a place where it can continue to warm you.
"Under normal conditions, when you're not exercising, about 50 percent of heat is lost through infrared radiation," lead study author Yi Cui, who researches materials science and engineering at Stanford University, told The Washington Post. No fabric on the market is totally permeable to this radiation. "If you could, in the summer time, make this radiation go out with nothing blocking it, you would feel cooler," he explained.
Cui and his colleagues actually published a paper over a year ago — in winter, naturally — where they showed that fibers woven from metallic nanowires could trap infrared radiation better than fabrics such as cotton, and keep bodies warmer as a result. "But cooling is much harder," he said.
Enter nanoPE, short for nanoporous polyethylene. Polyethylene is a common plastic, and the researchers were interested in it because infrared radiation can pass right through it when it's turned into cling wrap. But cling wrap also traps moisture, and it's see-through — so before it could be used in clothing, the researchers had to address a few things.
First, they found a nanostructure of polyethylene used in battery-making that is opaque to visible light while remaining transparent to infrared. That means it's not see-through but can still let infrared radiation through with ease. Then they developed a chemical cocktail to treat the plastic that made it permeable to water, like cotton is. To make the resulting plastic more fabric-like, they created a triple-layer material with two pieces of the polyethylene sandwiching a cotton mesh.
When they tested the material on surfaces of the same temperature as bare skin, it kept the experimental area almost 4 degrees cooler than cotton alone.
That might not sound like much, but it could be enough to help the environment. In an accompanying op-ed for Science, MIT's Svetlana Boriskina (who wasn't involved in the study) concludes that such a fabric could help cut down on air-conditioning usage. "Depending on the climate," Boriskina writes, "a 1 to 4 Celsius degree increase in the setpoint temperature could save up to 45% of the energy required for the building cooling."
That's been Cui's goal all along. "The main reason we use all of this energy cooling buildings is to keep the human bodies inside comfortable," he said. "We thought, why not cool the bodies instead?"
More work is needed to make nanoPe chic, comfortable and cost-effective at scale. Cui's first step is to make a woven version of the fabric. Right now, it's a solid, flat sheet, which feels odd against the skin.
"When you touch it, it’s soft, it’s flexible, and it almost feels like a regular fabric. What’s missing is that texture. A regular textile is not flat," Cui said. He and his team have actually already created a variant of the material made from interwoven fibers, but they're still in the process of testing to see whether it maintains the properties of the original fabric. He expects that work to be done in about a year and hopes that the material could be marketed a couple of years after that.
Here's to hoping we all look super cool in the summer of 2019.