Whitest paint
Barium sulphate paint
98.1 percentage
United States (West Lafayette)

Engineers at Purdue University in Indiana, USA, have developed an ultra-white paint incorporating barium sulphate particles that is up to 98.1% reflective. This compares to a reflectivity of 80–90% for other white paints designed to reflect sunlight that are currently available. Such paints are considered to be a potential game-changer for keeping the planet – particularly cities – cooler and reducing electricity use; buildings with a coating of this would need to rely far less on energy-hungry air conditioning. The findings were published in ACS Applied Materials & Interfaces on 15 April 2021.

This improved on a previous iteration developed at Purdue that used calcium carbonate particles which was 95.5% reflective. The new barium sulphate absorbs less than half the solar energy than that earlier version.

Seeking to highlight the potential benefits of radiative cooling, Professor Xiulin Ruan (who was part of the study) said: “If you were to use this paint to cover a roof area of about 1,000 square feet [93 m2], we estimate that you could get a cooling power up to 10 kilowatts. That’s more powerful than the air conditioners used by most houses.” Scaling that up, the scientists estimate that it would only require 0.5–1% of Earth’s surface to be coated in this paint (e.g., by painting roofs) to reverse global warming to date.