"The theory was put to the test last summer, with outdoor trials on the centre's rooftop in Tres Cantos, Madrid. After the material was subjected to ultraviolet light treatment that whitens it and improves its solar reflectance, the results came in: on the hottest, driest and sunniest days, the treated surface stayed up to 12.9°C cooler than a sample without coating."

This is fascinating. I hope I won'get downvoted for posting this comment on my post.