Prototype purple fabric reflects 87.6% of sunlight

Under direct sunlight, purple cotton usually faces a choice: absorb enough green light to look purple, or reflect the sun and stay cool. A team from Zhengzhou University and Adelaide University has built a prototype fabric that does both. In outdoor tests, it stayed 6.2°C cooler than commercially dyed purple cotton and 4.2°C cooler than commercial white cotton.

The material reflects an average 87.6% of solar radiation and emits 96.4% of mid-infrared radiation. That second property lets heat leave the fabric through the atmosphere toward outer space, the basic mechanism behind its passive cooling. Purple is difficult because producing the color requires absorbing green light, one of the strongest parts of the solar spectrum.

The researchers packed microscopic fibers with a purple metal-organic framework, or MOF, and zinc oxide nanoparticles. Together, the materials create the color while giving the textile its reflective and heat-emitting properties. When placed over simulated skin, the fabric lowered daytime temperature by up to 8°C, compared with 4.6°C for white cotton and 2.8°C for conventional purple cotton.

For people who work or exercise outdoors, the practical promise is straightforward: a colored garment could help manage body temperature without consuming additional energy, rather than forcing a choice between appearance and cooling. The textile is also lightweight, flexible, able to withstand significant stretching, permeable to water vapor such as perspiration, and highly water-repellent.

The limits are equally clear. These are outdoor material tests and simulated-skin measurements, not evidence that a finished garment is ready for widespread use. The fabric retained its cooling performance after 50 washing cycles and its optical performance after ultraviolet aging equivalent to roughly 108 days outdoors. They say the approach could be adapted to other colors by using different metal-organic frameworks.