Plastic wrap? Clothing of the future could cool our bodies
Stanford University scientists have invented a polyethylene fabric that actively draws heat away from the body, hoping that its cooling effect could reduce reliance on devices such as air-conditioning.
But what about those summer days when the sun beats down and the humidity ramps up and we find ourselves desperate to feel cooler? Stripping off can only achieve so much before modesty begins to suffer. So, we rely on adapting our environment, pumping up the air-conditioning or bathing in the breeze of a fan.
Yet researchers at Stanford University in California have invented a fabric that would actively cool our bodies, were it woven into clothing, potentially reducing our reliance on energy-thirsty devices that cool our buildings and vehicles.
The scientists’ thesis, published Friday in the journal Science, runs like this: About half our body heat is dissipated into the atmosphere via infrared radiation when we are at rest. Clothing and blankets that keep us warm in the colder months work by trapping this radiation.
But even light clothing designed specifically for summer captures much of that infrared energy, keeping us warm when we want to cool down. Even the synthetic fibers used in cutting-edge wicking technology that kicks into gear when we sweat, cooling us by drawing that water away from our skin, still trap the infrared radiation.
“The textile industry hasn’t paid much attention to the infrared radiation property of clothing,” Po-Chun Hsu, one of the Stanford researchers, told Smithsonian. “Specifically, transparency of infrared is an idea that has received very little research.”
The material chosen by the scientists to address this problem was polyethylene, known more commonly as kitchen wrap, cling film or Saran wrap. It has the perfect property of allowing infrared radiation to pass straight through, addressing the researchers’ central concern.
But it also has the unwelcome trait of being transparent with respect to visible light. And, as one of the other researchers, Shanhui Fan, said in a press release, “If dissipating thermal radiation were our only concern, then it would be best to wear nothing.”
Because most people do not want to appear naked in public, the Stanford scientists made use of a variant of polyethylene used in battery making, which has the added benefit of being opaque to visible light. Then they modified the chemical properties of the material to tackle the second stumbling block – the fact that polyethylene permits no water to pass through it.
Sandwiching a layer of cotton mesh between two sheets of the adapted polyethylene, to boost both strength and thickness, the team tested their invention. Placing it on a surface similar in temperature to our skin, they compared the amount of infrared energy passing through it to the levels able to penetrate a cotton fabric.
What they found was that their material allowed the surface to cool more than the simple cotton garment by 3.6 degrees F. While this may sound insignificant, Svetlana Boriskana, an expert in nanoengineering at the Massachusetts Institute of Technology in Cambridge, who was not involved in the study, wrote that such a shift could save up to 45 percent of the energy required for the building cooling, addressing one of the primary concerns of the Stanford group: to save energy by cooling a person’s body rather than their environment.
As Dr. Boriskana explains in the same opinion piece accompanying the paper, the basis for this new nanotechnology already has precedent – in nature. Specifically, she mentions the hairs smothering the body of the Saharan silver ant.
“The hairs are fine enough to strongly scatter and reflect sunlight to avoid overheating by absorption,” writes Boriskana. “At the same time, they are transparent at IR [infrared] wavelengths for shedding heat. Removal of the hairs increased the ant temperature by a couple of Celsius degrees.”
Work remains to be done before this material can be commercially viable, not least addressing the texture to make it feel more like the clothing we are accustomed to. But, as lead author Yi Cui tells The Washington Post, it could be as little as three years before we see garments made from his material hitting main street stores.