The world’s whitest paint, which has the ability to reflect about 98% of incoming sunlight, was created last year by Purdue University engineers using their knowledge of materials science. This paint has significant promise for improving building energy efficiency by reducing the need for air conditioning— something that becomes even more important as the world’s climate becomes more extreme. The team has since modified the recipe and created a thinner, lighter version, which they claim is perfect for usage on automobiles, trains, and airplanes.

“Cool” paint

The original ultra-white paint contained barium sulfate, a chemical component also found in photographic paper and cosmetics, which gave it its superior capacity to reflect sunlight. This was added to the mixture in the form of particles with variable sizes and light scattering abilities, allowing the paint to reflect a wider range of sunlight.

The material’s reflectivity of 98.1% was significantly higher than the 80–90% reflectivity of heat-reflecting paints that are typically sold commercially. The team conducted testing on outdoor surfaces and discovered that the paint might dramatically reduce surface temperatures relative to their surroundings and potentially offer cooling effects comparable to those of conventional air conditioners. But the paint had several drawbacks.

The paint’s creator, Xiulin Ruan, stated, “To achieve this level of radiative cooling below the ambient temperature, we had to apply a layer of paint at least 400 microns thick.”  Ruan goes on to explain that if you’re painting a sturdy and stationary structure, like the roof of a building, that level of thickness is acceptable— “but in applications that have precise size and weight requirements, the paint needs to be thinner and lighter.”

How the paint has improved

As a result, Ruan and his group developed a new formula. The new material, which is composed of hexagonal nanoplatelets of boron nitride, has layers that are only 150 microns thick and has a solar reflectance of 97.9%, slightly less than the original. That said, this new paint weighs about 80% less because it is not only thinner but has a lower density.

The benefits and potential applications of lighter paint

George Chiu, a mechanical engineering professor at Purdue, remarked, “This lightweight opens the doors to all kinds of applications… now this paint has the potential to cool the exteriors of airplanes, cars or trains. An airplane sitting on the tarmac on a hot summer day won’t have to run its air conditioning as hard to cool the inside, saving large amounts of energy. Spacecraft also have to be as light as possible, and this paint can be a part of that.”

Having applied for patents on the invention, the scientists revealed that they are currently in conversations to commercialize their paint and are excited about its potential uses.

“Using this paint will help cool surfaces and greatly reduce the need for air conditioning,” Ruan said. “This not only saves money, but it reduces energy usage, which in turn reduces greenhouse gas emissions. And unlike other cooling methods, this paint radiates all the heat into deep space, which also directly cools down our planet. It’s pretty amazing that a paint can do all that.”

Source study: Cell Reports Physical Science— Thin layer lightweight and ultrawhite hexagonal boron nitride nanoporous paints for daytime radiative cooling