The Whitest Paint Ever Could Block the Sun and Cool Earth

Caroline Delbert
·3 min read
Photo credit: Ryan McVay - Getty Images
Photo credit: Ryan McVay - Getty Images
  • The new whitest paint blocks 98.1 percent of sunlight and saves up to 10.5 degrees Celsius.

  • The paint is made with barium sulfate, an additive used in paper and makeup.

  • The material is mixed into normal-seeming, single-coat paint.

Scientists have unveiled the whitest paint ever—a paint so powerful, it can drop the temperature by whole degrees inside buildings, potentially eliminating the need for air conditioning. Could this new creation be a major weapon in the fight against climate change?

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Purdue University engineers made the paint, which consists primarily of barium sulfate, a compound used in cosmetics and ultrawhite paper products. Barium sulfate is extremely reflective, and that’s the key to making anything white: it must bounce away as much light as possible, rather than absorbing it, like the ultrablack Vantablack paint product.

The twist with this ultrawhite paint is the barium sulfate is also included in different particle sizes, which means more unpredictable surface area coverage that bounces even more light away.

The sky is the limit on pure white pigments in theory, but if the product is paint, it still has to hold together as, well, an effective paint product. That means the new paint reflects 98.1 percent of sunlight, which is a vast improvement over the team’s last iteration at 95.5 percent. Anything further, the scientists say, and the paint just wouldn’t work as paint anymore.

In their tests, the scientists used highly accurate temperature-reading equipment to see just how effective their paint was. The results:

The paint can keep surfaces 19 degrees Fahrenheit cooler than their ambient surroundings at night. It can also cool surfaces 8 degrees Fahrenheit below their surroundings under strong sunlight during noon hours.

The paint’s solar reflectance is so effective, it even worked in the middle of winter. During an outdoor test with an ambient temperature of 43 degrees Fahrenheit, the paint still managed to lower the sample temperature by 18 degrees Fahrenheit.

Photo credit: Purdue University/Joseph Peoples
Photo credit: Purdue University/Joseph Peoples

“If you were to use this paint to cover a roof area of about 1,000 square feet, we estimate that you could get a cooling power of 10 kilowatts,” Purdue professor Xiulin Ruan said in a statement. “That’s more powerful than the central air conditioners used by most houses.”

Making buildings as cool as possible isn’t just scientifically interesting—it’s gigantic business and also has an effect on climate change factors. If you put a dark-colored building in the desert and have to pay to cool it every day, this paint could save a large fraction of your cooling costs.

But more importantly, the right paint on a well-designed building could eliminate the need for air conditioning in some locations. “Radiative cooling is a passive cooling technology that offers great promises to reduce space cooling cost, combat the urban island effect, and alleviate global warming,” the researchers write in their new study, which appears in ACS Applied Materials & Interfaces.

They say their single-layer paint is the most effective product of its kind to date, replacing both costly (and less effective) heat-reducing paints, as well as more novel solutions like reflective metal plating. The ultrawhite paint works better and is likely easier to use, going on like regular paint—because it is just paint.

Photo credit: Purdue University/Jared Pike
Photo credit: Purdue University/Jared Pike

There’s an interesting question here about geoengineering, too. If the ultrawhite paint can reduce a building’s temperature by over 10 degrees Celsius, could ultrawhite particulate in the clouds help protect Earth from climate change?

The scientists’ previous whitest paint used calcium carbonate, the same material Harvard University’s Bill Gates-backed SCoPEx project planned to use in its controversial experiment to dim the sun before calling it off. The future may hold some clouds of barium sulfate.

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