China launches production of paint that cools walls by up to 25 degrees

Researchers at the Harbin Institute of Technology, working together with the company China Construction Zhonghuan, have developed a cooling paint capable of lowering the surface temperature of walls and storage tanks by up to 25 degrees Celsius. The technology has already moved out of the lab and into industrial-scale production, with an annual capacity of around 600,000 tonnes, according to Science and Technology Daily.

One of the first major tests took place at a petrochemical complex on Hainan Island, where the paint was applied to a giant liquefied gas storage tank. Such tanks heat up significantly in the sun, causing internal pressure to rise and increasing the risk of accidents — normally, they have to be cooled by spraying them with cold water using automated systems.

Test results exceeded expectations

According to Li Xiang, head of the China Construction Zhonghuan research centre, in sunny weather at 30°C the paint lowers the tank's surface temperature by roughly 25 degrees and the temperature inside the tank by nearly 7 degrees. Achieving the same cooling effect with water would require spraying around 35 tonnes of water per day.

The secret lies in passive radiative cooling: the coating reflects almost all incoming solar radiation while simultaneously releasing absorbed heat back into the atmosphere in the infrared range. The paint's reflectivity and radiative efficiency both reach around 97%. Over six months of testing, the coating withstood 40,000 wash cycles while losing less than 2% of its reflective properties — developers estimate the material's service life at 15 years.

Thinner than a sheet of paper

High reflectivity usually requires a thicker coating layer, which drives up production costs. Chinese engineers solved this problem by combining various inorganic particles with a structure resembling the folds of human skin. As a result, a layer just 100 micrometres thick — thinner than a sheet of office paper — is enough to do the job.

Scaling the lab formula up to an industrial production line proved no easy task: as production volumes increased, the distribution and size of the functional particles shifted, affecting the paint's optical properties. The team needed several months to refine the technology and ran dozens of trial batches. "In the lab, the challenge is to get something right once; on the production line, it's about repeating that ten thousand times without a single mistake," said Professor Wang Fuqiang of the Harbin Institute of Technology.

Similar work is underway in the West

Scientists around the world are developing similar cooling coatings. In 2021, researchers at Purdue University in the US unveiled a white paint based on barium sulfate particles that reflects up to 98.1% of sunlight and cools surfaces by about 4.4 degrees. In 2023, a team at the University of Maryland developed a microporous glass coating that lowers temperatures by up to 3.5 degrees. The University of New South Wales in Sydney presented a water-based roof paint that reduces temperatures by 6 degrees, while Spanish scientists from the Public University of Navarre and the University of the Basque Country achieved a 7.32-degree difference back in 2021.

The Chinese development originally grew out of research aimed at cutting building energy consumption: the less a surface heats up in the sun, the less heat enters the building, and the less often air conditioning needs to run. Whether the paint finds widespread use on residential buildings will only become clear after long-term use — price, as well as the coating's resistance to dirt, frost, rain and other weather effects, will all matter.

Source: novinky.cz