The whitest paint ever reflects 98% if sunlight and could cool homes.

Engineers created the whitest paint ever after 6 years of research. The new paint reflects 98% of sunlight and can cool surfaces by 4.5ºC (8ºF) below the ambient temperature. Counting buildings with this paint may reduce the need for air conditioning. Two features give the paint its extreme whiteness. One is the paint's very high concentration of a chemical compound called barium sulfate. Barium sulfate is a white crystalline solid that is odorless and insoluble in water. 

It is also used to make photo paper and cosmetics white. The second feature is that the barium sulfate particles are found in different sizes in the paint. Each particle spreads light depending on its size. Therefore, a wider range of particle sizes allows the paint to spread more of the light spectrum coming from the sun. Using high-accuracy temperature reading equipment called thermocouples. The researchers demonstrated that the paint can keep surfaces 8.5ºC (19ºF) cooler than their ambient surroundings at night. 

The paint's solar reflectance is so effective it even worked in the middle of winter. This white paint is the result of 6 years of research. Researchers considered over 100 different materials. Then they narrowed down their list to only 10 options. Then they tested about 50 different variations for each material. Their previous ultra-white paint was a formulation made of calcium carbonate. 

This is an earth-abundant compound commonly found in rocks and seashells. The researchers showed in this study that their barium sulfate-based paint can potentially handle outdoor conditions. The technique that is used to create the paint is also compatible with the commercial paint fabrication process making it potentially feasible to produce for large-scale adoption.