Materials

Whitest paint ever created could have air-con like cooling effects

Whitest paint ever created cou...
Study author Xiulin Ruan with his lab’s sample of the whitest paint on record
Study author Xiulin Ruan with his lab’s sample of the whitest paint on record
View 2 Images
Study author Xiulin Ruan with his lab’s sample of the whitest paint on record
1/2
Study author Xiulin Ruan with his lab’s sample of the whitest paint on record
An infrared camera image demonstrates how a sample of the whitest white paint can cool a board or surface below ambient temperature
2/2
An infrared camera image demonstrates how a sample of the whitest white paint can cool a board or surface below ambient temperature

The materials we coat our buildings with can have a big influence on their ability to reflect heat from the Sun and overall energy efficiency. Engineers at Purdue University have been at the cutting edge of this field of research for some time, and have just produced the whitest paint ever created, which they say reflects 98.1 percent of sunlight and can produce cooling effects that are on par with common air conditioners.

Upping the performance of white paints so that they reflect higher amounts of solar radiation is a common goal among researchers looking to keep living spaces cooler and lessen our reliance on air conditioners and other energy-intensive cooling systems. One NASA study from 2021 found that white coatings on New York City rooftops could reduce their peak temperatures by an average of 43 °F (24 °C), for example. We've also seen scientists cook up highly reflective paints made from glass, and others that incorporate Teflon to reflect up to 98 percent of incoming radiation.

The Purdue University scientists had recently shown off an ultra-white paint capable of reflecting 95.5 percent of sunlight. This material already far exceeds commercially available heat-reflecting paints that bounce away 80 to 90 percent of sunlight, but now the researchers are upping their game even further.

Their new ultra-white paint owes its excellent performance to a careful mix of particles made from barium sulfate, which is a chemical compound used in white photographic paper and cosmetics. These particles can make the paint very white and very reflective, but there is a line to be drawn in terms of compromising its performance, with too high a concentration causing the paint to peel off or break apart.

But by varying the size of the particles, the scientists can alter each one's ability to scatter light, with a wider range of particle sizes resulting in a paint that can scatter more of the light spectrum coming from the Sun. The team has now landed on just right recipe to produce the whitest paint ever made, and therefore the coolest paint on record.

“A high concentration of particles that are also different sizes gives the paint the broadest spectral scattering, which contributes to the highest reflectance,” says Joseph Peoples, a Purdue Ph.D. student in mechanical engineering.

An infrared camera image demonstrates how a sample of the whitest white paint can cool a board or surface below ambient temperature
An infrared camera image demonstrates how a sample of the whitest white paint can cool a board or surface below ambient temperature

The paint was put to the test outdoors where it was found to keep surfaces 19 °F (10.5 °C) cooler than their ambient surroundings at night time, and 8 °F (4.5 °C) cooler under strong sunlight during the middle of the day. In one outdoor test during the middle of winter in ambient temperatures of 43 °F (6.1 °C), the paint lowered the temperature of a surface by 18 °F (10 °C).

“If you were to use this paint to cover a roof area of about 1,000 square feet (93 sq m), we estimate that you could get a cooling power of 10 kilowatts," says Xiulin Ruan, a Purdue professor of mechanical engineering. "That’s more powerful than the central air conditioners used by most houses."

The research was published in the journal ACS Applied Materials & Interfaces.

Source: Purdue University

8 comments
Steve White
good well lets paint trillions of helium balloons with it and release them to mitigate the warming.
stevendkaplan
Paint one surface with Vantablack and another with this barium paint and use the resulting temp difference to run a sterling Engine for power.
ljaques
Huh? "New, improved white paint, now with Photon-repelling Teflon!" ? Yeah, buddy!
Username
It prevents the surface from getting hot. That is not the same as cooling it, which is removing heat from it.
Rick Bowman
Umm, why not just put a mirror down?
bwana4swahili
Nice idea BUT the real problem is keeping 'white' clean!
TechGazer
Right, it doesn't cool, but it does provide less solar gain than dark materials. I replaced a brown asphalt shingle roof with white metal, and it made a very big difference in avoiding overheating indoors. Their statement is misleading marketing though, probably comparing their paint vs the best heat-absorbing paint, rather than vs common white roofing.

They don't mention how reflective it is after a years of exposure to the elements.
RangerJones
TechGazer is correct. What they do to measure emissivity is compare a white listed at [grade 100]/black and they list it @say- 25. Nothing has been comparably affected/tested. Would be like saying a dog is much more like a wolf than a cat is to a jaguar.