http://www.digitaljournal.com/tech-and-science/science/ready-for-a-long-hot-summer-self-cooling-clothing-could-help/article/490902

Ready for a long, hot summer? Self-cooling clothing could help

Posted Apr 22, 2017 by Tim Sandle
University of California San Diego scientists have developed a low-cost plastic material which can act as the base material for clothing that cools down the wearer.
A selection of clothes  adorned by models  at the autumn 2016 London Fashion Weekend.
A selection of clothes, adorned by models, at the autumn 2016 London Fashion Weekend.
The science behind the fabric is that it allows the human body to discharge body heat in two ways which allows the person wearing the fabric to feel cooler. By ‘feeling cooler’ this is in comparison to wearing cotton clothing. The textile is part of a new family of fabrics.
The heat discharge mechanisms are: letting perspiration evaporate through the material and allowing heat that the body emits as infrared radiation to pass through the plastic textile. While some fabrics allow for perspiration to evaporate no material, suitable for use as clothing, allows infrared radiation to pass through.
Heat can be transferred from place to place by conduction, convection and radiation. With infrared radiation objects emit and absorb infrared radiation. This means the hotter an object is (like the human body), the more infrared radiation it emits. Typically 40 to 60 percent of body heat is infrared radiation. This is the reason someone quickly becomes warm when they wrap a blanket around themselves; while this might be good for camping, it isn’t so good when wearing clothes in the summertime.
To develop the new fabric the researchers first used computer models. This led to a nanotechnology process that led to the development of a form of polyethylene. The material allows for thermal radiation, air and water vapor to pass through. By allowing a large quantity of infrared radiation to pass through, the rate of cooling increased.
Having developed the material, various stages were gone through to improve the material. This focused on the optical properties of the nanoporous polyethylene, which was key to finding ways to maximize the amount of infrared radiation that passed through the material. This was down to getting the pore size right.
Commenting on the success of the fabric, Professor Yi Cui, who led the research, said: "If you can cool the person rather than the building where they work or live, that will save energy.” The end product is a three-ply version of the material whereby two sheets of treated polyethylene are separated by a cotton mesh for strength and thickness. The material has been tested out on people and the temperature of the skin of the people wearing the material recorded.
The new textile is described in the journal Science. The research paper is titled “Radiative human body cooling by nanoporous polyethylene textile.”