A new purple fabric developed by researchers in China and Australia stayed as much as 6.2°C cooler than conventional purple cotton in direct sunlight, suggesting that cooling textiles may not have to be limited to white.
Most passive cooling fabrics are white because they reflect sunlight away from the body. Darker fabrics generally absorb more solar energy, making cooling more difficult. Purple presents an additional challenge because its color comes from absorbing green light, which is a strong part of the solar spectrum.
Researchers from Zhengzhou University, with involvement from Adelaide University, developed a fabric designed to retain its purple appearance while reflecting much of the sunlight that reaches it. The work was led by researchers from Zhengzhou University and included Adelaide University researchers.
The fabric uses microscopic fibers containing a purple metal-organic framework, or MOF, along with zinc oxide nanoparticles. The combination gives the material its color while providing properties that help it shed heat.
The fabric reflected an average of 87.6% of solar radiation and emitted 96.4% of mid-infrared radiation. That infrared emission allows heat from the fabric to escape through the atmosphere toward outer space.
Outdoor tests compared purple and white cotton
The researchers tested the material outdoors under direct sunlight. The new purple fabric was 4.2°C cooler than commercial white cotton and 6.2°C cooler than commercially dyed purple cotton.
They also tested how the fabric affected a simulated skin surface. During the day, simulated skin covered by the new material was up to 8°C cooler than uncovered simulated skin. White cotton produced a maximum reduction of 4.6°C, while conventional purple cotton produced a maximum reduction of 2.8°C.
The results indicate that the new material’s cooling performance did not depend on giving up its purple color.
“We have traditionally had to make a choice between cooling performance and appearance,” said Jun Ma, a materials engineer at Adelaide University’s School of Chemical Engineering and a co-author of the paper.
“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 material was tested for everyday textile properties
The researchers also examined several properties relevant to clothing. The fabric was lightweight and flexible, could withstand significant stretching, and allowed water vapor, including perspiration, to pass through.
It was highly water-repellent and retained its cooling performance after 50 washing cycles. The material also provided strong UV resistance and retained its optical performance after high-intensity UV aging equivalent to about 108 days outdoors.
Yangzhe Hou, a doctoral candidate in Adelaide University’s School of Chemical Engineering and a co-author, said the researchers are interested in fabrics that can help manage body temperature without using additional energy.
The researchers say the approach could potentially be adapted to other colors by using different metal-organic frameworks with different optical properties. That could allow cooling fabrics to be made in a broader range of colors.
The study was published in Small.
