Say goodbye to your air conditioners and desk fans, instead keep yourself cool with...paint?
That's right - coating your house in the world's whitest paint could help stave off the summer heat and save the world at the same time.
According to the engineers at Purdue University who created the paint, it would eliminate our need for air conditioning by sending heat away from a building instead of absorbing it. Naturally, if a building doesn’t get hot, we won’t need to use power-hungry machines to cool us down.
They estimate that only 0.5–1% of Earth’s surface (e.g. building roofs) would need to be coated in this paint to reverse global warming to date.
This new ultra-white formulation can be considered the yang to the yin of ‘Vantablack’, the blackest black. Vantablack absorbs up to 99.9% of visible light, whilst the whitest paint reflects up to 98.1% of sunlight.
“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. That’s more powerful than the central air conditioners used by most houses,” explained Xiulin Ruan, a Purdue professor of mechanical engineering.
In addition to cooling your house, the paint could also cool the Earth's surface. According to the researchers, applying the paint to roads, rooftops and cars would offset some effects of the greenhouse gases they create.
“We’re not moving heat from the surface to the atmosphere. We’re just dumping it all out into the universe, which is an infinite heat sink,” said Xiangyu Li, who worked on this project as a Ph.D. student in Ruan’s lab.
So what actually makes the whitest paint so white?
The same chemical compound which is used to make white photo paper and cosmetics – barium sulfate. The high concentration of this compound gives the paint its intense whiteness.
“We looked at various commercial products, basically anything that’s white. We found that using barium sulfate, you can theoretically make things really, really reflective, which means that they’re really, really white.” - Xiangyu Li
Additionally, the barium sulfate particles in the paint are all different sizes. Particles scatter different amounts of light depending on their size, so having a variety of sizes ensures that the paint scatters more of the light spectrum.
“A high concentration of particles that are also different sizes gives the paint the broadest spectral scattering, which contributes to the highest reflectance,” explained Joseph Peoples, a Purdue Ph.D. student in mechanical engineering.
It’s possible to make the whitest paint even whiter, but not without sacrificing its quality. Achieving an even higher reflectance is pointless if ultimately the paint can’t be brushed, sprayed, or rolled with appropriate viscosity.
“Although a higher particle concentration is better for making something white, you can’t increase the concentration too much. The higher the concentration, the easier it is for the paint to break or peel off,” Li said.
The paint’s cooling effects have been measured in a range of outdoor conditions. It can keep surfaces 19°F cooler than their surrounding temperature at night and 8°F cooler under strong sunlight. It even worked during winter!
“It’s very counterintuitive for a surface in direct sunlight to be cooler than the temperature your local weather station reports for that area, but we’ve shown this to be possible,” – Xiulin Ruan
The whitest paint features in the Rebuilding Earth section of Guinness World Records 2022
Header image credit: Purdue University/Jared Pike; Joseph Peoples