The coating was inspired by a technique that people employ to keep their homes cool in summer.
In today’s world, comfort means clothing that can adapt to changing climates, keeping you warm or cool as needed. Researchers, supported by the American Chemical Society (ACS), have developed a new chalk-based coating for fabrics that can reduce body temperature by up to 8 degrees Fahrenheit. This innovation uses limestone crystals, known for their natural cooling properties, to achieve the effect.
Evan D. Patamia, a lead researcher and student at the University of Massachusetts, presented this breakthrough at the ACS Fall meeting in August 2024. Previously, Patamia had been working on building a range of fabrics that could conduct the process of “radiative cooling,” implying that the fabric deflects the sun’s rays while simultaneously pushing out body heat. Materials like titanium dioxide or aluminum oxide are light-reflecting materials, whereas some organic polymers require the addition of chemicals to be able to reflect the light. So, Patamia and his fellow researcher Megan Yee asked themselves the question, “Can we develop a textile coating that does the same thing using natural or environmentally benign materials?”
Trisha L. Andrew, a chemist and materials scientist working with Patamia, said, “If you walk out into the sunlight, you will get increasingly hot because your body and clothing are absorbing ultraviolet (UV) and near-infrared (near-IR) light from the sun.” However, limestone crystals can reflect both UV and IR light, helping to keep you cool.
Andrew and Patamia conceived the idea of using limestone after being inspired by the plasters that people use to keep their houses cool during summers. In an elaborate process, Patamia and Yee created a mixture of calcium carbonate, the main component in limestone, chalk, and bio-compatible barium sulfate to coat the polymer.
Once the chemical solutions were ready, the researchers ripped small squares of fabric and repeatedly dipped some of them in the solution. With each dip, the crystals became smoother, creating a matte-like sheen on the squares. After this task, the researchers stowed away the treated and untreated fabrics into their bags and headed out to take a stroll outside in the sun as temperatures went up to 90 degrees Fahrenheit. In the middle of the afternoon, they analyzed the effects of the sun on the two kinds of fabrics and were excited to note the result. “We see a true cooling effect,” said Patamia. “What is underneath the sample feels colder than standing in the shade.”
What’s even more interesting about this chalk-based coating is that it doesn’t get wiped away from a garment when the fabric is washed. “What makes our technique unique is that we can do this on nearly any commercially available fabric and turn it into something that can keep people cool,” concluded Patamia. “Without any power input, we’re able to reduce how hot a person feels, which could be a valuable resource where people are struggling to stay cool in extremely hot environments.”
“Personal cooling textiles show great promise to tackle heat-related impacts of climate change,” Xueping Zhang, a professor specializing in personal thermal-moisture management at Donghua University, China, told CNN. “With the advancement of materials and technology, personal cooling textiles (will) be available for general public use in the near future,” added Zhang.
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