Plastic cloth makes for cooler clothing

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Stanford researchers began with a sheet of polyethylene and modified it with a series of chemical treatments, resulting in a cooling fabric(Credit: Stanford University/L A Cicero)

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Unless you're into bleeding-edge haute couture, wrapping yourself in cling film isn't likely to be your first choice in summer fashion. This might change your mind. A team from Stanford University has developed a new low-cost textile made of plastic that uses a combination of nanotechnology, photonics, and chemistry to cool the wearer in a new way, leaving them feeling almost four degrees Fahrenheit cooler compared to cotton clothing.

Fabric is very good at keeping people warm, but doesn't do so well when it comes to keeping them cool. That's because the only mechanism that textiles have for cooling is evaporation. As the wearer perspires, the cloth wicks the sweat away to the surface, where it evaporates.

One problem is that this means that fabrics can't cool someone until they actually start sweating. Another is that natural and synthetic fabrics are opaque to infrared rays, which means they hold in heat like a vacuum flask.

"Forty to 60 percent of our body heat is dissipated as infrared radiation when we are sitting in an office," says Shanhui Fan, a professor of electrical engineering who specializes in photonics. "But until now there has been little or no research on designing the thermal radiation characteristics of textiles."

Cooling with plastic

At first glance, polyethylene, which is used in everything from electrical insulation to sandwich bags, is the last thing to use to make clothes because it has the reverse problem of conventional cloth. The plastic is transparent to infrared radiation, but it's waterproof and airtight, so wearing a shirt made out of polyethylene is an uncomfortable, sweaty experience.

It's also a bit embarrassing because polyethylene is transparent to visible light.

What the Stanford team did was to re-engineer polyethylene so that it still lets out infrared radiation, but can breathe, so it cools in both the traditional and a way that hasn't been tried before.

The team started out with a type of polyethylene that's used in making batteries, which is opaque to visible light, yet still transparent to IR. They treated it with benign chemicals to alter the structure of the plastic so that instead of being a solid sheet, it had a nanoporous structure that allowed water vapor molecules to pass through, so it breathes like natural fibers.

Nano structure in the plastic used to allow perspiration and infrared waves to escape (Credit: Stanford University)

To make the plastic more like regular cloth and give it more strength and thickness, the researchers turned it into a three-ply by adding a second layer of plastic separated from the first by a cotton mesh.

The new fabric was compared with a swatch of cotton fabric by placing both on a surface designed to mimic the warmth of human skin. When measured, the new plastic cloth made the skin surface 3.6º F (2.7° C) cooler than cotton.

The Stanford team is currently working on adding new colors and textures to the material to make it more cloth-like, as well as finding ways to make it cheap to manufacture. In addition, the plastic fabric could point to new ways to cool or heat objects without outside sources of energy.

Another aspect of the new cloth is that it could potentially help save money on air conditioning by making people hold off switching on the cooler.

"If you can cool the person rather than the building where they work or live, that will save energy," says Yi Cui, an associate professor of materials science and engineering at Stanford.

The research was published in Science.

The animation below explains how the plastic cloth works.

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