Scientists made a paint so white it can keep a building cooler than the air around it, even under the midday sun.
Researchers at Purdue University created the whitest paint on record. It reflects 98.1% of sunlight, and it entered the Guinness World Records.
Normal white paint warms up in the sun. Even commercial heat-reflecting paints reflect only about 80 to 90% of sunlight and still absorb heat.
The secret is barium sulfate, a mineral packed into the paint at very high levels, with particles of different sizes to scatter almost every part of sunlight. It also sends heat out as infrared radiation into the sky.
In tests, painted surfaces stayed about 8°F cooler than the surrounding air under strong midday sun, and up to 19°F cooler at night.
The lead researcher estimates that covering a roof of around 1,000 square feet could give about 10 kilowatts of cooling, more than most home air conditioners, without using any electricity.
A coat of paint could one day do the job of an air conditioner.
(Source: Purdue University, April 15, 2021 / ACS Applied Materials & Interfaces)