Stanford researchers began with a sheet of polyethylene and modified it with a series of chemical treatments, resulting in a cooling fabric.
If this textile is woven into clothing, it can keep the body cooler than what is possible with synthetic or natural fabrics used in present day clothes.
The researchers believe that this new family of textiles may become the basis for garments that keep people cool in hot weather without air conditioning.
The Stanford material makes the user feel nearly 4°F cooler than if they wore cotton clothing, by allowing the body to emit heat in two ways. By letting sweat evaporate via the material, the body is kept cool, which is something other fabrics do. However the innovative material offers a second mechanism, where heat is emitted from the body as infrared radiation to pass via the plastic textile.
Every object, including the human body, emits heat in the form of infrared radiation, which is an invisible and gentle wavelength of light. A blanket helps to keep the body warm by trapping infrared heat emissions close to the body. The thermal radiation leaving the body makes the person visible in the dark when viewed via night-vision goggles.
The Stanford team combined photonics, chemistry, and nanotechnology to create polyethylene with several desirable features for clothing material.
The simplest feature was the ability of infrared radiation to pass through the material, which is the characteristic of basic polyethylene food wrap. However, kitchen plastic cannot be used for clothing as it is see-through and impervious to water.
First, they discovered an alternative of polyethylene widely used in battery manufacture, which has a specific nanostructure that is transparent to infrared radiation but opaque to visible light.
This would potentially allow body heat to escape, and could make a base material.
They then treated the polyethylene using benign chemicals to facilitate water vapor molecules to evaporate via nanopores in the plastic, letting the plastic to breathe in the same manner as a natural fiber.
They developed a three-ply version – two sheets of treated polyethylene divided by a cotton mesh for thickness and strength, to make the thin material feel a lot like a fabric.
To examine the cooling potential of their three-ply model against a cotton fabric with similar thickness, they placed a small piece of each material on a warm surface similar to the warmth of bare skin and measured the amount of heat each material trapped.
The cotton fabric made the skin surface 3.6°F warmer than the Stanford cooling textile.