Coating clothes with this simple material could cool your body by up to 8 degrees

By Billy Stockwell, CNN

(CNN) — Spending time outside during a heat wave can be sweaty, uncomfortable, even health-endangering, but scientists have come up with an innovation they say could provide relief: clothes that physically cool down the body.

Researchers at the University of Massachusetts Amherst have developed a flexible, chalk-based coating which can be added to fabrics. During tests in scorching summer heat, they found it reduced the temperature underneath clothes by up to 8 degrees Fahrenheit compared to the air, and by up to 15 degrees compared to untreated fabrics.

This innovation is one of a number of efforts to turn people’s clothes into a tool against extreme heat, which is intensifying as humans continue to burn planet-heating fossil fuels. Heat is the deadliest type of extreme weather, causing heat exhaustion and even heat stroke, a potentially fatal illness where the body loses the ability to cool itself down.

The UMass researchers say they wanted to develop a way to cool fabric using an environmentally benign material. Inspired by traditional limestone-based plasters used to cool homes in hot climates, they coated fabric tiles with particles of calcium carbonate – the main component in limestone and chalk.

The coating was able to both reflect the sun’s energy back into the atmosphere, as well as allow the wearer’s natural body heat to escape, according to their new study, currently being peer-reviewed, which was presented to the American Chemical Society this month.

“We start with your cotton T-shirt… and we just apply this coating on either one or both faces of the fabric,” Trisha L. Andrew, a chemist and materials scientist at UMass, told CNN. “The coating is entirely surface level. It does not penetrate or change the cotton fibers,” she added.

The coating can be applied to nearly any commercially available fabric and can also be put through the washing machine, the scientists say.

“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,” Evan Patamia, a graduate student at UMass who worked on the innovation, said in a statement.

Cooling fabrics are not a new invention, but past designs have often involved rigid structures, complex manufacturing processes and electrical components, according to a 2023 scientific review of cooling fabric research, making them uncomfortable to wear and expensive.

The UMass development is part of a growing body of research exploring cheaper, comfier and more scalable alternatives as the threat of extreme heat around the world grows.

Scientists at RMIT University in Melbourne, Australia, have used tiny particles called nanodiamonds to coat cotton fabric, resulting in a temperature drop of up to 3 degrees Celsius (5.4 Fahrenheit) compared to untreated cotton, according to a recent study.

This may not sound huge, but it makes “a difference in comfort and health impacts over extended periods, and in practical terms could be the difference between keeping your air conditioner off or turning it on,” Shadi Houshyar, project lead and a senior lecturer at RMIT, said in a statement.

The RMIT University study found that using cooling fabrics could lead to a 20 to 30% energy saving due to lower use of air conditioning, which is a hugely climate-polluting cooling tool.

Nanodiamonds may sound expensive, but researchers say they are not the same as the diamonds used in jewelry. “They’re actually cheap to make,” Houshyar said.

There are still improvements to be made, she added. For example, they found the efficiency of the nanodiamond fabric decreased after the fabric was washed multiple times.

The nanodiamonds work in a similar way to the limestone particles UMass is using, Houshyar told CNN. The principle of these studies is the same, she said, using nanoparticles to transfer heat away from the body.

Houshyar – who has researched protective clothing for over a decade – said the production process used by UMass was promising but they would need to work out how to scale it up and keep costs low.

Cooling fabrics must be affordable, she said. “If the cost is triple times the cost of the normal fabric, it’s not going to be enough for everyone to use it.” It is often the poorest people who are among the most vulnerable to extreme heat and have the least access to cooling technologies.

As more products enter the market, there is “a lot of opportunity in this area to scale it up to make it available to everyone,” Houshyar added.

UMass’s Andrew said her team had been limited so far by the size of their laboratory equipment. Through a new startup company, however, they aim to start a pilot production, making treated fabric sheets that are 5 feet wide and 300 feet long.

The costs of the raw materials for the coating are “low to manageable,” Andrew said, but accepted the overall price would increase slightly due to the application process, during which the coating is applied to the fabric.

If it proves possible to scale up the production of affordable cooling fabrics, some researchers say the benefits could extend far beyond clothing.

Scientists at the University of Chicago hope their cooling fabric, made from materials including silver nanowire and wool, could also be used to cool buildings and cars. In tests under the fierce Arizona sun, they found the fabric stays 16 degrees Fahrenheit cooler than commercial silk fabric often used in summer clothing.

Using cooling fabric more widely would reduce the costs and climate impact of air conditioning, the scientists said. “Our civilization actually uses about 10 to 15% of the energy in total just to make ourselves feel comfortable wherever we go,” Po-Chun Hsu, a University of Chicago molecular engineering professor and a study author, said in a statement.

While tackling extreme heat means rapidly reducing the burning of fossil fuels, deadly heat waves are already here, and some scientists believe these cooling fabrics can play a useful role as more people are exposed to heat their bodies can struggle to tolerate.

“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, who was an author on the 2023 scientific review of cooling fabrics.

They “can provide localized cooling to specific body regions with high accuracy,” she added, and can be tailored for different environments.

She sees a large-scale role for cooling fabrics — and soon. “With the advancement of materials and technology, personal cooling textiles (will) be available for general public use in the near future.”

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