World’s whitest paint wins award

Author Cutting Tool Engineering
July 17, 2023 - 11:00am

The whitest paint, which was developed by researchers at Purdue University and recognized by Guinness World Records Ltd., has won the 2023 Innovation Award in the sustainability category from SXSW LLC.

Led in development by Xiulin Ruan, professor of mechanical engineering, the paint fights global warming by keeping surfaces cool enough to reduce the need for internal air conditioning. SXSW is the latest organization to recognize the innovation, which has been featured on “PBS NewsHour” and “The Late Show With Stephen Colbert.” The paint also was the winner of the 2023 Gizmodo Science Fair.

 Xiulin Ruan, professor of mechanical engineering, holds up his lab’s sample of the whitest paint on record.
Xiulin Ruan, professor of mechanical engineering, holds up his lab’s sample of the whitest paint on record. Image courtesy of Purdue University/John Underwood

Last year, Ruan and his team innovated further by developing a formulation of his groundbreaking paint that is thinner and lighter — ideal for radiating heat away from cars, trains, airplanes and even spacecraft. According to his team’s models, covering 1% of Earth’s surface in the technology could mitigate the total effects of global warming, a fact encouraging the team to continue pursuing formulas suitable for surfaces like asphalt and roadways.

Typical commercial white paint becomes warmer rather than cooler when subjected to sunlight or other light sources. Paints on the market that are designed to reject heat reflect only 80% to 90% of sunlight and can’t make surfaces cooler than their surroundings. In comparison, the whitest paint reflects 98.1% of solar heat away from surfaces.

Because the paint absorbs less heat from the sun than it emits, a surface coated with this paint is cooled below the surrounding temperature without consuming power.

Using this formulation to cover a roof area of about 1,000 sq. ft. could result in a cooling power of 10 kW, more powerful than the air conditioners used by most houses. At SXSW, researchers demonstrated the effects of the difference with two model barns sitting under direct halogen lights: one painted in commercial paint and one in Purdue’s white paint. Judges were able to compare thermometers reading the barns’ internal temperatures and to feel the difference in the roofs. The barn painted in Purdue’s technology consistently held cooler internal temperatures by 8 to 10 degrees Fahrenheit. The “whitest white” barn roof was also much cooler to the touch, prompting many surprised responses from judges and viewers.

While Ruan’s original paint formula was massively efficient, it required a layer 0.4 mm thick to achieve subambient radiant cooling. The newer, thinner formulation achieves similar cooling with a layer just 0.15 mm thick.

The new paint also incorporates voids of air, which make it highly porous. This lower density, together with the thinness, provides another huge benefit: reduced weight. The newer paint weighs 80% less than the original paint yet achieves nearly identical solar reflectance of 97.9% compared with the original formula’s 98.1%. 

— Trevor Peters