On a hot tarmac in the peak of summer, an airplane’s crew has little choice but to run the air conditioner to keep themselves and their passengers cool. But soon, crews could become less reliant on the A.C., thanks to a new lightweight, ultra-white paint that can reflect up to 97.9 percent of sunlight.
This engineered paint has the potential to cool the exteriors of airplanes, cars, trains and even spacecraft. As the planet warms because of human-caused climate change, the paint could be an innovative, passive way to keep spaces—and people—cool. At the same time, it could reduce our reliance on energy-guzzling and heat-emitting air conditioners that contribute to global warming.
The paint is an improvement on an earlier formula, which was too thick to be applied to anything but stationary structures. Now, researchers say they’ve refined the paint with an ultra-thin formula that’s safe for coating vehicles. In a paper published Monday in the journal Cell Reports Physical Science, the team shared the details of their new-and-improved product.
In spring last year, a team from Purdue unveiled the first ultra-white paint—a product so white that it set a Guinness World Record. The key was barium sulfate, which allowed the paint to reflect 98.1 percent of sunlight and cool surfaces by up to 19 degrees Fahrenheit compared to their surroundings.
For comparison, commercially available paints on the market today can only reflect 80 to 90 percent of sunlight, meaning they absorb a lot more light and heat. The ultra-white paint, meanwhile, cools surfaces by emitting more heat than it retains—and it doesn’t use any electricity.
“Air conditioners can cool your house, but they move the heat from inside the house to outside—the heat is still in the city, it’s still on the Earth,” said Xiulin Ruan, a mechanical engineer at Purdue who helped develop the paint, to Smithsonian magazine last year. “Our paint does not use any power, but, more importantly, it sends the heat to space. The heat doesn’t stay on the Earth, so that really helps the Earth to cool down and can stop the warming trend.”
To achieve those groundbreaking results, however, the engineers had to paint a layer that was at least 400 microns thick. That thickness works for strong, stationary structures, like the roof of a building or home. But for vessels that move, as well as objects with specific size and weight requirements, the paint really needs to be thinner and lighter, according to the researchers.
So, the engineers went back to the lab and began tinkering with the paint’s chemical composition. Their new paint uses hexagonal boron nitride, a substance often used in lubricants, to give it a blindingly white hue. The hexagonal boron nitride scatters sunlight to reflect up to 97.9 percent of the sun’s rays, and it gets applied at a thickness of just 150 microns. The new paint is also highly porous, with voids of air that helped drop its weight by about 80 percent compared to the earlier version, per the researchers.
Making the paint lighter and thinner should, in theory, make it useful for a wider array of applications. In the time since the first paint came out, Ruan has been contacted by spacecraft manufacturers, architects and makers of clothes and shoes who were looking for a lighter-weight version, per the statement. Ruan says the team is currently in discussions to commercialize the paint.
Widespread adoption should, in theory, make it an even more viable tool for combating climate change in the long run, researchers say.
“The paint has the benefits of saving on electric bills and at the same time contributing to saving the earth,” University of Tennessee Knoxville mechanical engineer Xiangyu Li, who helped develop the paint while studying at Purdue but is not an author of the new paper, said to the Indianapolis Star's Sarah Bowman last year. "It connects with everyone.”