Did you know that super white paint could help keep your home cooler without needing air conditioning, which saves energy and reduces the heat in cities?
This innovation is part of a growing field of “radiative cooling” technology. It uses materials to cool buildings by reflecting sunlight and releasing heat into the sky, which can cut down on energy use and help fight climate change.
What Is Radioactive Cooling?
Radiative cooling is a way to cool things down by using the heat that objects naturally give off. Just like how our bodies radiate heat, so do things like buildings and cars. The technique is to make something that can release more heat than it takes in from the sun.
Purdue University scientists have created an ultra-white paint that does just that. The paint allows the surface to shed the sun’s heat and cool itself down without needing any extra energy. This could mean a big change in how we stay cool, like being able to replace air conditioners and save a lot of energy.
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Breakthrough in Radiative Cooling with BaSO₄-Based Paints & Films
In this study, researchers show that BaSO₄ (barium sulfate) nanoparticle films and BaSO₄-acrylic paints provide effective full-day cooling. BaSO₄ has properties that minimize sunlight absorption and maximize heat release.
This new version improves on an earlier Purdue paint made with calcium carbonate, which reflected 95.5% of sunlight. The barium sulfate in the new paint absorbs less than half as much solar energy as the previous version. (ref)
With optimized particle sizes, the BaSO₄ film reflects 97.6% of sunlight and cools more than 40.1°F (4.5°C) below the surrounding temperature, with an average cooling power of 117 W/m². The BaSO₄-acrylic paint, with a solar reflectance of 98.1%, achieves similar cooling and is durable, easy to apply, and compatible with standard paint production. (ref)
What Gives the White Paint Its Whiteness & Coolness
According to the Purdue researchers, the paint’s extreme whiteness comes from two main features. First, it has a high concentration of BaSO₄, the compound that’s also used to make photo paper and cosmetics white.
Xiangyu Li, a researcher at MIT who worked on the project at Purdue said that they have “looked at various commercial products, basically anything that’s white.” They found that barium sulfate makes things highly reflective, which makes them very white.
The second feature is that the BaSO₄ particles are different sizes. The size of each particle affects how much light it scatters, and having a range of sizes helps the paint scatter more of the sunlight’s spectrum.
Also, the paint’s whiteness makes it “the coolest on record”. Using thermocouples, the researchers showed that outdoors, the paint can keep surfaces 19°F cooler than the surrounding air at night. It can also cool surfaces 8°F below the surroundings during strong midday sunlight.
The paint’s solar reflectance works even in winter. In an outdoor test at 43°F, it lowered the surface temperature by 18°F.
According to Purdue, this white paint is the result of six years of research, building on efforts since the 1970s to create radiative cooling paint as an alternative to traditional air conditioners. (ref)
Purdue Paint Sets a World Record for Whiteness
The paint, developed at Purdue University by Professor Xiulin Ruan and his graduate students, earned a Guinness World Records™ title. (ref)
Ruan’s lab tested over 100 materials, narrowed them down to 10, and created about 50 formulations for each. While breaking the record for the whitest paint wasn’t their main goal, the researchers aimed to fight global warming.
“When we started this project seven years ago, our focus was on saving energy and combating climate change,” said Dr. Ruan, a Purdue mechanical engineering professor, in a podcast episode of “This Is Purdue.” (ref)
The paint has also won the 2023 Innovation Award in the sustainability category at the South by Southwest Conference & Festivals (SXSW). The award, given for exciting creative developments, was presented to Purdue on March 13 at the 25th annual SXSW Innovation Awards Ceremony in Austin, Texas. (ref)
The researchers have already teamed up with a company to mass-produce the paint and put it to market. Patent applications for the paint have been filed through the Purdue Research Foundation Office of Technology Commercialization.
Davin is a jack-of-all-trades but has professional training and experience in various home and garden subjects. He leans on other experts when needed and edits and fact-checks all articles.