Researchers have developed a cloth that reflects sunlight and also allows heat radiating from a person's body to escape, thereby removing major forms of heat from a person's body.
Experts noted the development of "cooler" clothing for hot summer days has remained challenging. This is because the human body emits mid-infrared (IR) radiation in the wavelength range that partially overlaps with that of the visible light spectrum at normal skin temperatures of 34°Celsius.
The result is that cloth blocking visible light often traps in body heat.
Po-Chun Hsu, Yi Cui and colleagues explored an existing nanoporous polyethylene (nanoPE) to evaluate if it allows IR-radiation to pass through, and thus make a likely cool clothing candidate.
NanoPE has interconnected pores that are 50 to 1000 nanometers in diameter. These diameters are comparable in size to the wavelength of visible light, and thus capable of scattering it or reflecting it back.
At these sizes, the pores are much smaller than the wavelength of infrared light, meaning nanoPE is still highly transparent to IR.
The team tested nanoPE and cotton, finding the former allows 96% of IR to pass through, compared to its cotton counterpart, which only permitted the passage of 1.5% of infrared waves.
Regular polyethylene lets similar amounts of IR through, but the nanoPE significantly outperforms this traditional cloth in reflecting visible light, at 99% opacity compared to 20%.
In experiments with a device that mimics the heat output of human skin, the authors found that nanoPE only heats the simulated skin temperature by 0.8°C compared with a heat boost of 3.5°C for cotton and 2.9°C for commercially available polyethylene fabrics.
Researchers were also able to enhance fluid wicking of the nanoPE using a microneedle punching technique and by coating the material with a water-repellent agent. Normal polyethylene doesn't wick away moisture well.