Scientists in the US have developed a paint significantly "whiter than the whitest paint currently available".
Tests carried out by researchers at Purdue University on their "ultra-white" paint showed it reflected more than 98% of sunlight.
That suggests, the scientists say, that it could help save energy and fight climate change.
Painting "cool roofs" white is an energy-saving approach already being rolled out in some major cities.
Commercially available white paints reflect between 80% and 90% of sunlight, according to lead researcher Prof Xiulin Ruan from Purdue, in West Lafayette, Indiana. "It's a big deal, because every 1% of reflectance you get translates to 10 watts per metre squared less heat from the Sun," he explained.
"So if you were to use our paint to cover a roof area of about 1,000 sq ft (93 sq m), we estimate you could get a cooling power of 10 kilowatts. That's more powerful than the central air conditioners used by most houses," he said.