White paint has been used for decades to reduce the sun's heat that rooftops absorb, thereby
keeping the building cooler than it would be if painted in a dark color. However, a new ultra-
white paint shows evidence of cooling buildings. In fact, the roof's surface temperature is
lower than the air temperature immediately surrounding the roof.

The cooling is made possible because the new ultra-white paint reflects 98% of the sun's rays
plus sends infrared heat away from the surface. As proof, according to their research, tests
conducted during sunny, midday hours on the roof of a campus building in West Lafayette,
Indiana, the paint kept outdoor surfaces 8 degrees cooler than the surrounding ambient
temperatures. At night, the paint kept surfaces 19 degrees cooler than their surroundings.

Currently, there are white paints on the market made with titanium dioxide, which reflects
specific wavelengths of sunlight. But, they absorb the sun's ultraviolet rays, causing the painted
surface to heat up.
The new paint is made with barium sulfate, a known UV-reflecting compound used in
cosmetics, reflective photo paper, oil paints, x-ray examinations, etc. The barium sulfate
particles in the paint vary in size, making the sun's rays "scatter," explains Xiulin Ruan, a Purdue
mechanical engineering professor.
White paint has been used for decades to reduce the sun's heat that rooftops absorb, thereby keeping the building cooler than it would be if painted in a dark color. However, a new ultra- white paint shows evidence of cooling buildings. In fact, the roof's surface temperature is lower than the air temperature immediately surrounding the roof. The cooling is made possible because the new ultra-white paint reflects 98% of the sun's rays plus sends infrared heat away from the surface. As proof, according to their research, tests conducted during sunny, midday hours on the roof of a campus building in West Lafayette, Indiana, the paint kept outdoor surfaces 8 degrees cooler than the surrounding ambient temperatures. At night, the paint kept surfaces 19 degrees cooler than their surroundings. Currently, there are white paints on the market made with titanium dioxide, which reflects specific wavelengths of sunlight. But, they absorb the sun's ultraviolet rays, causing the painted surface to heat up. The new paint is made with barium sulfate, a known UV-reflecting compound used in cosmetics, reflective photo paper, oil paints, x-ray examinations, etc. The barium sulfate particles in the paint vary in size, making the sun's rays "scatter," explains Xiulin Ruan, a Purdue mechanical engineering professor.