Researchers at Purdue University have developed an "ultra-white" paint that reflects 98 per cent of sunlight and deflects infrared heat, allowing buildings to cool below the surrounding air temperature.
The paint, which the university describes as the "whitest paint on record", owes its cooling power to barium sulphate ? a pigment derived from the mineral barite ? and reflects up to 98.1% of sunlight.
Top image: Xiulin Ruan holding a sample of the paint. Above: infrared photographs show that the paint cools a surface below the ambient temperature
Unlike the titanium dioxide used in traditional white paints, which absorbs UV light, the barium sulphate is also capable of deflecting infrared heat away from the surface to which it is applied. The researchers used barium sulphate in a high concentration of 60 per cent and in pigment particles of various sizes, which allows the paint to scatter more of the light spectrum from the sun.

"A high concentration of particles that are also different sizes gives the paint the broadest spectral scattering, which contributes to the highest reflectance," explained Joseph Peoples, a Purdue University PhD student in mechanical engineering.
This is what allows the paint to cool a surface below its surrounding air temperature, unlike other reflective white paints on the market which generally reflect 80 to 90 per cent of sunlight while absorbing infrared heat.
A higher concentration of barium sulphate would likely...