When the weather gets extremely hot, wearing white or light-colored clothing is often recommended because these colors reflect more sunlight.
Darker and brighter colors usually absorb more solar energy and become warmer.
But researchers in China and Australia have developed a purple fabric that could change that rule.
The new high-tech textile can stay up to 6.2°C cooler than ordinary purple cotton under direct sunlight.
The research, led by scientists at Zhengzhou University with researchers from Adelaide University, was published in the journal Small.
Creating colorful cooling clothing is difficult because color itself depends on absorbing certain wavelengths of visible light. Purple is particularly challenging because purple materials absorb green light, which makes up a strong part of the sun’s energy.
To overcome this problem, the researchers created microscopic fibers containing a purple material known as a metal-organic framework, or MOF, together with zinc oxide nanoparticles. The combination produces a purple appearance while allowing the fabric to reflect most of the sun’s energy.
Tests showed that the material reflects about 87.6% of incoming solar radiation. It also emits 96.4% of mid-infrared radiation. This second property is important because objects naturally release heat as infrared radiation. A material that releases this radiation efficiently can lose heat more easily instead of trapping it.
Outdoor experiments produced impressive results. Under direct sunlight, the new purple material was 4.2°C cooler than commercial white cotton and 6.2°C cooler than conventionally dyed purple cotton.
Researchers also tested how well the fabric could protect something resembling human skin. Simulated skin covered with the new fabric was up to 8°C cooler during the daytime than uncovered simulated skin. White cotton reduced the temperature by a maximum of 4.6°C, while ordinary purple cotton achieved a reduction of only 2.8°C.
The researchers say the material could eventually be useful for outdoor workers, athletes and other people who spend long periods in hot conditions. Because the cooling process does not require electricity, clothing made from such materials could help people manage heat without using additional energy.
The fabric also appears practical enough for everyday use. It is lightweight, flexible and able to stretch. Water vapor from perspiration can pass through it, while its surface strongly repels liquid water. Importantly, it maintained its cooling ability after 50 washing cycles.
It also provided strong protection against ultraviolet radiation and continued to perform well after laboratory UV testing designed to simulate about 108 days of outdoor exposure.
The researchers believe the technology could eventually extend beyond purple. By using different metal-organic frameworks with different optical properties, scientists may be able to produce cooling fabrics in many colors.
That could lead to a future in which staying cool in the summer no longer means having to dress in white.
