Researchers at the University of California have managed to paint a roof and wall paint that is whiter than freshly fallen snow. The weatherproof paint reflects 98 percent of sunlight and is designed to keep homes cool in an increasingly hot climate in an inexpensive and energy-efficient manner.

"If you wear a white T-shirt on a hot, sunny day, it feels cooler than a shirt with a darker color. That's because the white shirt reflects more sunlight. It works the same with buildings," said Aaswath Raman, materials science teacher at the University of California Los Angeles.

Together with colleagues from Columbia University in New York, Raman conducted tests with a newly designed paint. Applied to the outside of buildings, it gives a strong cooling effect, making the indoor temperature even lower than the ambient temperature.

Ordinary white paint does absorb invisible light

The secret of the paint is that it not only reflects visible light, thereby preventing it from converting energy into heat, but also direct heat radiation from the sun and other objects - the infrared part of sunlight. We cannot see this light with our eyes, but we can feel it with our skin.

"Finnish research showed last year that air conditioners worldwide already use almost as much power as is generated by all solar panels together."

Regular white paint contains titanium oxide and reflects about 85 percent of the visible sunlight. However, this paint absorbs infrared radiation, as well as ultraviolet radiation - which also comes from the sun. The maximum reflective paint is based on the mineral barite and also contains Teflon.

The findings were published in the journal Joule . The researchers hope that their paint can offer an alternative to the growing use of air conditioners.

Finnish research last year showed that air conditioners worldwide are already using almost as much power as is generated by all the solar panels combined - and that this energy demand could grow by as much as 35 times in this increasingly warmer century, also driven by growing prosperity and population growth in warm, sunny areas.

“A dark roof ensures a lower gas bill in winter. Ideally, your house will change color with the seasons. ”

Old and effective 'cooling trick' not yet standard

In an earlier interview with NU.nl, the Delft urban sustainability professor Andy van den Dobbelsteen therefore also argued for cooling on the outside of buildings. Not with ultra-white paint, but an even more classic solution: sun protection.

This should be included as standard with climate-proof new construction, but that is not yet the case, according to Van den Dobbelsteen. Modern, well-insulated houses therefore threaten to become too hot in the summer sun.

In winter you prefer a dark roof again ...

Whether the ultra-white paint is also beneficial in the relatively cool Dutch climate remains to be seen. In the winter six months, we try to make our houses warmer than the outdoors.

And although the sun is lower and more often hidden behind clouds, with a dark roof you should still have a somewhat lower gas bill. Ideally, your house will change color with the seasons.