A plastic-based textile material that could efficiently cool the body in hot surroundings has been developed in the USA, paving the way for ‘air-conditioning’ clothing that could cut cost of temperature management in buildings in future.
The polyethylene-based fabric, described in an article in the journal Science, allows the human body to discharge heat so efficiently that a person wearing clothes made of this material would feel nearly 4 degrees Fahrenheit (2.2°C) cooler than if they were wearing cotton clothes.
"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.
The key to the supercooling properties of the new material lies in the two-way process that allows heat to be removed from the body. In addition to perspiration evaporating through the material, typical for conventional fabrics, the new material also allows the body heat to be emitted as infrared radiation.
"Forty to 60 per cent of our body heat is dissipated as infrared radiation when we are sitting in an office," said Shanhui Fan, a professor of electrical engineering, "but until now there has been little or no research on designing the thermal radiation characteristics of textiles."
The researchers started their quest for the self-cooling material with an ordinary polyethylene food wrap. This material allows infrared radiation to pass through, although it prevents perspiration from evaporating. It is also transparent, which is not convenient for use in textile design.
However, some nano-level engineering allowed the team to achieve the desired properties.
Instead of an ordinary kitchen wrap, the team used a different type of polyethylene, used in batteries, as a base material. This type of polyethylene has a nanostructure that prevents visible light from passing through but is still permeable to infrared radiation.
Further chemical treatment enabled the researchers to create nanopores in the plastic material that enable water vapour molecules to pass through.
To make this thin material more fabric-like, the researchers created a three-layer structure with two sheets of the treated polyethylene with a cotton mesh in the middle for extra strength and thickness.
Small samples of the material were then placed on a warm surface together with a piece of cotton fabric.
The comparison showed that the cotton fabric made the skin surface 3.6 F warmer than the cooling textile. The researchers said this difference means that a person dressed in clothes made of the new material might feel less inclined to turn on a fan or air conditioner.
However, there is still a long way to go before the material can be of any practical use.
"If you want to make a textile, you have to be able to make huge volumes inexpensively," Cui said.
The researchers hope the material will advance the field of passive cooling, which could lead to considerable energy savings compared to current approaches.
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