The new paint reflects 98% of sunlight as well as radiating infrared heat through the atmosphere into space. In tests, it cooled surfaces by 4.5C below the ambient temperature, even in strong sunlight. 

Currently available reflective white paints are far better than dark roofing materials, but only reflect 80-90% of sunlight and absorb UV light. This means they cannot cool surfaces below ambient temperatures. The new paint does this, reducing the need for air conditioning and the emissions they produce.

“If you look at the energy [savings] and cooling power this paint can provide, it’s really exciting,” said Xiulin Ruan, a Purdue mechanical engineering professor whose team published its results in the journal ACS Applied Materials & Interfaces.

Three factors aid the paint’s cooling performance. First, barium sulphate was used as the pigment which, unlike titanium dioxide pigment, does not absorb UV light. Second, a high concentration of pigment was used – 60%. Third, the pigment particles were of varied size.

The amount of light scattered by a particle depends on its size, so using a range scatters more of the light spectrum from the sun. Ruan’s lab had assessed more than 100 materials and tested about 50 formulations for each of the most promising

The researchers said the paint could be on the market in one or two years.