It’s a hot day in September with not even a whisper of a breeze disturbing the trees outside. Your clothes stick to you in the heat and you reach to turn on the fan beside you. At this point, the worst thing you can imagine is wearing an outfit made of cling-film. Yet a team of engineers in America have suggested just that.
Researchers at Stanford University have created a cheap, plastic-based fabric, ideal for clothing. The team suggest their new material can cool the body up to 4 degrees Fahrenheit more than natural or synthetic fabrics. The idea is to keep cool in hot climates without needing to turn up the air conditioning.
“If you can cool the person rather than the building where they work or live, that will save energy,” said Yi Cui, an associate professor of materials and engineering and of photon science at Stanford.
How does it work?
The plastic material features a carefully engineered structure that cools the body in two different ways. Firstly, the fabric contains a series of tiny holes, or pores, which allow water to escape. This works in much the same way as regular fabrics, letting the body breathe and cool as you sweat.
The material really comes into its own however with its next trick. All objects throw off heat in the form of infrared radiation, an invisible and harmless wavelength of light. You can see this perfectly when you look through a thermal imaging camera. In the picture, the hottest areas shine brightly against a cool, dark background.
Regular clothing traps this radiation against the body, insulating the wearer. This is why in a thermal image a person’s clothes show up much darker than their exposed hands and face. The new material’s revolutionary cooling mechanism allows body heat to escape as infrared light through the plastic.
When it came to creating their super-cool clothing, the engineers found inspiration in cling-film. The thin polyethylene food wrapping is perfectly designed to let infrared pass through, making it handy to have in the kitchen. Its other properties however are less desirable. As well as stopping air and water escaping, the plastic is also completely see-through. This is not an ideal clothing option!
Solving the problems
To overcome these barriers, the team turned to industry to help them out. First, they found a variant of the plastic, often used for making batteries. While infrared could still get through the industrial cling-film, visible light could not. This plastic did still block air and water, making wearing an outfit of the stuff a very sweaty experience. The team solved this problem by treating the polyethylene with harmless chemicals. This created nanopores in the fabric to let out any water vapour molecules. With the extra holes, the fabric could breathe, much like a natural fibre.
A thin sheet of cling-film however – even if it is no longer see-through and sweaty – is still a far cry from a high-tech performance material. To make it more fabric-like, the team sandwiched a cotton mesh between two layers of the treated plastic.
The beauty of the fabric, say its creators, is in its simplicity and availability. “If you want to make a textile, you have to be able to make huge volumes inexpensively,” Cui said. The base material for the fabric is already mass produced for the battery industry. This could make it much quicker and easier to develop the material into a consumer-ready product.
The team believe that their research can open the door to the future of low-energy heating and cooling solutions, simply by tuning materials to dissipate or trap their infrared radiation.
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