Chinese researchers at Stanford University have developed a plastic-based textile that can cool the human body and may someday reduce demand for air conditioning.
The material cools by not only taking away sweat like ordinary fabrics do, but also allowing heat that the body emits as infrared radiation to pass through, which makes the wearer feel 35.6 degrees Fahrenheit cooler than they would when wearing cotton clothes, according to the researchers' study, recently published in the journal Science.
By cooling the person rather than the entire building, a substantial impact could be made on global energy use, according to Yi Cui, an associate professor of materials science and engineering at Stanford and lead author of the study.
At the normal skin temperature of 93 degrees Fahrenheit, the human body emits mid-infrared radiation, an invisible and benign wavelength of light, which contributes to more than 50 percent of the total body-heat loss in a typical indoor scenario like an office.
However, traditional textiles are not designed for infrared radiation control.
To enhance radiative dissipation in hot weather, the researchers found nanoporous polyethylene (nanoPE), a variant of polyethylene widely used in battery-making, which allows infrared radiation to pass through it while being opaque to visible light.
There are also other challenges that the researchers need to address besides ensuring the cooling effect, such as wicking, mechanical strength and air permeability, which are important for a textile to be wearable.
The researchers altered nanoPE through a number of processes in order to make it a suitable human cloth.
They first created microholes as small as human hair with commonly used microneedle punching, resembling the spacing between the yarns in woven cotton textile.
Because the hole is so small, the visual opacity is not affected. The wicking rate and the mechanical strength of the new material also are comparable with cotton, according to the study.
To make the thin material more fabric-like, the researchers created a three-layer material with two sheets of treated polyethylene sandwiching a cotton mesh for strength and thickness.
They then tested the cooling effect of nanoPE with a device that simulated the heat output of skin. The material increases the simulated skin temperature by 33 degrees Fahrenheit, compared with 38 degrees for cotton.
Though the temperature difference is small, it can be the air conditioner setpoint difference, said the researchers, which means the person dressed in the new clothing material may not feel the need to turn on the air conditioner.
The study also suggests that more work needs to be done to explore the potential wearability modification methods on the new material, such as textures and coloration.
