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Reflective paint confirmed as world’s whitest

Xiulin Ruan have created the whitest paint on record. (Photo: John Underwood)

USA: A paint that reflects up to 98.1% of sunlight and could cool surfaces 4.5ºC below ambient has earned a Guinness World Records title as the world’s whitest paint.

The paint, developed at Purdue University in the USA, appears in the 2022 edition of Guinness World Records. 

“When we started this project about seven years ago, we had saving energy and fighting climate change in mind,” said Xiulin Ruan, a professor of mechanical engineering at Purdue.

Ruan invented the paint with his graduate students. The idea was to create paint that would reflect sunlight away from a building. Making this paint really reflective, however, also made it really white. The formulation that Ruan’s lab created reflects 98.1% of solar radiation at the same time as emitting infrared heat. 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.

Typical commercial white paint gets warmer rather than cooler. Paints on the market that are designed to reject heat reflect only 80%-90% of sunlight and can’t make surfaces cooler than their surroundings.

Using this new paint formulation to cover a roof area of about 1,000ft2 could result in a cooling power of 10kW, Purdue researchers showed in a published paper. 

This white paint is the result of research building on attempts going back to the 1970s to develop radiative cooling paint as a feasible alternative to traditional air conditioners. Ruan’s lab had considered over 100 different materials, narrowed them down to 10 and tested about 50 different formulations for each material.

Two features make this paint ultra-white: a very high concentration of a chemical compound called barium sulfate – also used in photo paper and cosmetics – and different particle sizes of barium sulfate in the paint. What wavelength of sunlight each particle scatters depends on its size, so a wider range of particle sizes allows the paint to scatter more of the light spectrum from the sun.

Related stories:

White paint is coolest yet16 April 2021
USA: Engineers at Purdue University say they have created a white paint that reflects up to 98.1% of sunlight and could cool surfaces 4.5ºC below ambient even under the noon-day sun. Read more…

Radiative cooling paint could reduce the need for air conditioning – 22 October 2020
USA: Engineers at Purdue University have created a white paint that is said to be able to keep surfaces up to 18ºF (10ºC) cooler than ambient. Read more…

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