A purple cooling fabric developed by Chinese and Australian researchers has been shown to stay cooler than conventional purple cotton in direct sunlight, in findings that could expand options for passive cooling clothing beyond the typical reliance on white materials.
According to a study led by Zhengzhou University and involving Adelaide University, the fabric stayed up to 6.2°C cooler than commercially dyed purple cotton when exposed to direct sunlight. Researchers said coloured fabrics are harder to cool because darker shades absorb more solar energy, and purple is particularly challenging because it is produced by absorbing green light, a strong part of the solar spectrum.
Adelaide University Professor Jun Ma, a co-author and materials engineer in the School of Chemical Engineering, said the researchers aimed to show cooling performance does not need to come at the expense of colour. “We have traditionally had to make a choice between cooling performance and appearance,” Ma said. “Our research shows that we can have both. We can make a fabric that looks purple, but at the same time reflects most of the sun’s energy and releases heat very efficiently.”
The fabric was produced using microscopic fibres containing a purple metal-organic framework (MOF) material and zinc oxide nanoparticles. The researchers reported the fabric reflects an average 87.6% of solar radiation and emits 96.4% of mid-infrared radiation, a mechanism intended to allow heat to dissipate through the atmosphere.
In outdoor testing under direct sunlight, the fabric was reported to be 4.2°C cooler than commercial white cotton and 6.2°C cooler than commercially dyed purple cotton. The researchers also reported that simulated skin covered with the new fabric was up to 8°C cooler than uncovered simulated skin during the day, compared with a maximum reduction of 4.6°C for white cotton and 2.8°C for conventional purple cotton.
Adelaide University co-author Yangzhe Hou, a PhD candidate in the School of Chemical Engineering, said potential applications include people who spend extended periods outdoors. “For outdoor workers, athletes and anyone exposed to hot weather, staying cool is not just about comfort,” Hou said. “We are interested in developing fabrics that can help manage body temperature without consuming additional energy.”
The researchers said the fabric is lightweight and flexible, can withstand significant stretching, and allows water vapour to pass through. They also reported the fabric is water-repellent, retained cooling performance after 50 washing cycles, and maintained optical performance after high-intensity UV ageing testing equivalent to about 108 days outdoors.
The research was published in the journal Small (DOI: https://doi.org/10.1002/smll.74745). The researchers said the approach could potentially be adapted to other colours by using different metal-organic frameworks with different optical properties.
