All objects, including our bodies, release heat in the form of infrared radiation, an invisible and harmless wavelength of light.
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Engineers have created clothing for a warming world – a fabric that allows your body heat to escape far better than other materials do.
“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 science and engineering and of photon science at Stanford University, California, who led the study.
Researchers have engineered a low-priced plastic material that could become the basis for clothing that keeps people cool in hot climates.
Existing fabrics already do a good job of taking moisture away from the body, but the issue is more “how do you control the infrared radiation coming out of the human body”, he said.
It is this combination of blocking visible light and allowing IR to pass through that distinguishes the nanoPE material from regular polyethylene, which allows similar amounts of IR to pass through, but can only block 20 percent of the visible light compared to nanoPE’s 99 percent opacity.
Majority of the heat that radiates off human body at normal skin temperature is in the infrared portion of the light spectrum. That’s where clear clingy plastic kitchen wrap comes in.
The researchers developed a plastic-based textile that could be woven into fabric for clothing to help people in hot climates stay cool without air conditioning. The researchers used a sheet of polyethylene and applied a series of chemical treatments, which resulted in a cooling fabric.
First, they found a variant of polyethylene commonly used in battery making that has a specific nanostructure that is opaque to visible light yet is transparent to infrared radiation, which could let body heat escape.
“We processed the material to develop a textile that promotes effective radiative cooling while still having sufficient air permeability, water-wicking rate, and mechanical strength for wearability”, the researchers wrote in their study.
The material is transparent to human body infrared radiation, opaque to visible light, and permeable to perspiration vapour. To give it more structure, they then made a three-ply version, wedging a thin cotton mesh between two sheets of polyethylene. The researchers said that the difference means that a person wearing the new material would feel less inclined to use a fan or air conditioner.
‘If dissipating thermal radiation were our only concern, then it would be best to wear nothing’.
Wearers would feel almost 4 degrees Fahrenheit cooler in the new material than in cotton clothing, according to the report.
This resulted in a material that met the criteria of the researchers.
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. Adapting a material already mass produced for the battery industry could make it easier to create products.
They also treated it with chemicals that enable the evaporation of water vapor molecules through the nanopores in the plastic, which makes the textile breathable like a natural fiber.
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Prof Fan added: “In hindsight, some of what we’ve done looks very simple, but it’s because few have really been looking at engineering the radiation characteristics of textiles”.
