In the heat of summer, anyone spending time outdoors—be it athletes, landscapers, children at the park, or beachgoers—can benefit from a fabric designed to keep cool. Although some materials can reflect sunlight or disperse heat, they usually involve high-end fibers or intricate manufacturing. Recent studies reveal a sturdy chalk-based coating that can lower the temperature of the air beneath treated fabric by as much as 8 degrees Fahrenheit.
During the peak summer heat, anyone who enjoys the outdoors—like athletes, landscapers, children playing, or beachgoers—could take advantage of cooling fabric. There are textiles available that can reflect sunlight or draw heat away from the body, but these often rely on specialized fibers or intricate manufacturing processes. Now, researchers have unveiled a chalk-based coating that can reduce the airflow temperature underneath treated fabric by up to 8 degrees Fahrenheit.
Evan D. Patamia, a graduate student at the University of Massachusetts Amherst, will share the findings of their team at the upcoming fall conference of the American Chemical Society (ACS).
“When you step into the sun, your body and clothing can absorb harmful ultraviolet (UV) and near-infrared (near-IR) radiation, making you feel hotter,” explains Trisha L. Andrew, a chemist and materials scientist collaborating with Patamia. “Plus, our bodies continuously generate heat, which can also be seen as a form of light.”
To enhance outdoor comfort, researchers are creating textiles that both reflect sunlight and release body heat—this process is called radiative cooling. Some of these materials include light-refracting synthetic particles like titanium dioxide or aluminum oxide embedded in the fibers. Others rely on organic polymers, like polyvinylidene difluoride, but these often involve the use of perfluoroalkyl and polyfluoroalkyl substances—commonly referred to as PFAS or forever chemicals—in their production.
However, scaling up the production of these textiles for mass distribution is not environmentally sustainable, according to Andrew. She challenged team members Patamia and Megan K. Yee by asking, “Can we create a fabric coating using natural or eco-friendly materials that achieves the same results?”
Previously, Andrew and her team had developed a straightforward method to apply long-lasting polymer coatings to fabrics known as chemical vapor deposition (CVD). This approach combines the synthesis and application processes, allowing for a thin polymer layer to be grafted onto commercial textiles with fewer steps and lower environmental impact compared to other coating methods.
Drawing inspiration from the crushed limestone-based plasters traditionally used to keep homes cool in extremely sunny regions, Patamia and Yee set out to innovate a process to incorporate calcium carbonate—found in limestone and chalk—along with bio-compatible barium sulfate into the polymer applied via CVD. Calcium carbonate particles are effective at reflecting visible and near-infrared wavelengths, while barium sulfate particles reflect UV light.
To create the treated fabric, the researchers took small fabric squares and coated them with a 5-micrometer-thick layer of poly(2-hydroxyethyl acrylate). They then repeatedly immersed these polymer-treated squares into solutions containing calcium or barium ions along with solutions of carbonate or sulfate ions. With each immersion, the crystals would grow larger and more uniform, giving the fabric a chalky, matte finish. Patamia notes that by adjusting the number of dips, the particles can be optimized to achieve the best size distribution—between 1 and 10 micrometers in diameter—for effectively reflecting both UV and near-IR light.
The team assessed the cooling capabilities of both treated and untreated fabrics outdoors on a sunny day, with temperatures exceeding 90°F. They recorded air temperatures beneath the treated fabrics that were up to 8°F cooler than the surrounding air during the hottest afternoon hours. The cooling effect was even stronger at times, with instances reaching a 15°F difference between the treated and untreated fabrics, which caused the untreated fabric to warm the air underneath it. “We’re observing a real cooling effect,” Patamia states. “What’s under the sample feels cooler than simply standing in the shade.”
To further evaluate the durability of the mineral-polymer coating, Yee simulated normal wear and tear from laundry detergent in a washing machine. She discovered that the coating didn’t wear off and maintained its cooling properties.
“Currently, our capabilities are limited by the size of our lab equipment,” Andrew remarks. She is involved with a startup that is working to scale the CVD process for larger fabric panels, approximately 5 feet wide and 100 yards long. Andrew believes this project could help translate the work of Patamia and Yee into production on a larger scale.
“What sets our method apart is that we can apply this to nearly any commercially available fabric, transforming it into something that effectively keeps people cool,” concludes Patamia. “Without needing any external power source, we can lessen the heat felt by individuals, which could provide significant benefits in extremely hot climates.”
This research was funded by the U.S. National Science Foundation, and Trisha L. Andrew is engaged in commercializing the polymer coating technique.
