What should you wear to keep cool on a hot day? One word: plastics.
A form of polyethylene — the common plastic that makes up ClingWrap — is a promising candidate for a textile that prevents us from overheating, researchers say. Hopefully, it won’t look like those PVC bodysuits that pop up every Halloween.
Many researchers are trying to create cooling fabrics, from cloth inspired by squid skin to electroactive textiles. But the team led by Yi Cui, a materials scientist at Stanford University, was inspired by materials that we don’t usually consider for clothing. In a study published today in Science, the team turned a battery component into a textile that lets our body’s natural heat escape better than cotton. The team hasn’t worn the fabric themselves yet, but Cui insists it feels “very much like normal fabric” and hopes it will be commercialized within two years.
The human body naturally emits infrared radiation — this is why we show up on heat maps — but even “cool” fabrics like cotton and linen trap this radiation and keep us hot. One material lets that heat out: polyethylene, but no one wants to wear ClingWrap because it’s thin (and see-through). So plain polyethylene won’t work, but Cui’s team proved that a different, opaque form can still keep us cool. If their idea catches on, it might even help reduce global warming: if we stay cool with clothing, we might not rush to turn on the AC and create more greenhouse emissions.
“One of the biggest impacts we hope to have is to reduce air conditioning, save energy inside a building, and then reduce climate change,” says Cui. “But we also just hope to make people feel more comfortable in warm weather or when they exercise.”
This form of plastic wrap is called “nanoporous polyethylene” (nanoPE for short). It’s stiffer and has pores the right size to let infrared radiation pass through to keep us cool, while trapping visible light so it’s not transparent.
NanoPE is easily available and often used in lithium batteries to separate the positive and negative sides and prevent electrical shorting. Cui’s team improved nanoPE to make it suitable for clothing. First, they added a chemical called polydopamine that lets water pass more easily through the nanoPE, so that sweat can evaporate quickly. Punching holes in the material made it easier for air to pass through and the fabric slightly more “breathable.” Finally, they stuck some cotton mesh between two layers of the nanoPE to make it stronger.
The team’s unusual choice of material is innovative, says Prabhakar Bandaru, a professor of nanoengineering at the University of California-San Diego. “It’s definitely fascinating that they took some non-fabric material used for batteries and used it for something totally different,” he says.
Cui himself says that it took so long to think about the possibilities of nanoPE as a textile because “the people working on textiles and the people working on batteries almost never overlap.” His own research is on batteries, but two years ago he became interested in saving energy by reducing AC, and so began to also work on thermal textiles. It was only then, he says, that “it suddenly occurred to me that a battery separator might be the way to go.”
Cui’s hunch turned out to be right. To test the material, scientists put it on what is essentially a hot plate set to the temperature of human skin. They recorded the default (human skin) temperature, and then how much hotter the plate became after being covered by nanoPE, compared to cotton and a material called Tyvek often used in protective gloves. The nanoPE was nearly 5 degrees Fahrenheit cooler than the cotton, and 4 degrees Fahrenheit cooler than Tyvek.
The next step is to figure out how to weave nanoPE for greater strength and comfort. The main challenge, according to Bandaru, is comfort and selling buyers on the idea. “Cotton is very comfortable, but if you are asked to wear plastic I would imagine that it may not be as comfortable,” he says. “If someone asked us to wrap plastic around us, our first inclination is ‘why’?”
Still, Bandaru notes that the research opens interesting possibilities. For example, nanoPE could potentially be used to make an adaptive garment that wouldn’t just cool, but could let out more or less body heat depending on whether someone was in shade or in the hot sun. So that could be the answer to why we’d want to wrap plastic battery parts around us: the most comfortable shirt ever.