Scientists have created an ultra-white pigment, which is the yin of Vantablack's yang. 

Although today's ultra-black materials can absorb more than 99.96% of sunlight, this new ultra-white coating can reflect 95.5% of all photons that hit it.

Objects coated with this new type of acrylic material will not heat up under direct light, and can keep the temperature lower than the surrounding temperature even in the sun, which can provide a new energy-saving way to control the temperature inside the building.

The other “insulation coatings” we currently have can only reflect 80% to 90% of the sunlight and cannot reach below ambient temperature.

Xiulin Ruan, a mechanical engineer at Purdue University in Indiana, said: “Developing a sub-environmental radiant cooling solution that provides a convenient single-layer particle matrix coating format and high reliability is a long-lasting task.”

"This is essential for the widespread application of radiant cooling and the mitigation of global warming effects." 

In the summer, many modern buildings rely on air-conditioning devices to discharge the heat inside the building to the outside. This, together with the excess heat generated by the strong energy required to achieve cooling, helps turn cities into "heat islands" and further exacerbate global warming.

Radiant cooling is a passive technology that can reflect the heat of a building into space, but it is more difficult to achieve than radiant heating.

Since the 1970s, scientists have been trying to figure out how to reflect enough sunlight so that passive cooling is more effective than active air conditioning. 

Recently, some people have even tried to assemble "reverse solar panels", which can capture some of the emitted heat and convert it into energy even at night.

But these are still just concepts, and it is not clear whether these devices can really work outside of pure simulation. 

Painting residential and commercial buildings ultra-white may be a more feasible method, at least in the near future.

This new type of acrylic paint is made of calcium carbonate fillers with high particle concentration and multiple sizes, which can effectively scatter all wavelengths of the solar spectrum.

The matrix of the paint also has a vibration resonance peak, which ensures that a large amount of heat is reflected outwards-much faster than other cooling paints can achieve.

In two-day field tests in different locations and various weather conditions, the researchers tested the radiant cooling capacity of the coating and found that it can scatter 95.5% of the sunlight and keep the ambient temperature 10 degrees Celsius below the ambient temperature at night, at least below The ambient temperature is 1.7 degrees Celsius at noon.

Compared with the surface coated with the same thickness of commercial white paint, the temperature of the object covered in the calcium carbonate paint in the infrared lens is much lower.

More importantly, the paint is applied and dried in almost the same way, and it is wear-resistant, waterproof, and can withstand outdoor weathering for at least three weeks, although longer trials are currently underway.

"Our coatings are compatible with the manufacturing process of commercial coatings, and the cost may be equivalent or even lower," Ruan said. 

"The key is to ensure the reliability of the coating to make it feasible in long-term outdoor applications." 

The authors say that their coating is "the best reported radiant cooling performance," although they admit that when reviewing their results, another team published a paper that the cooling coating should contain a high concentration of wide band gap particles.

They also suggested adding fluorocarbon polymers, which have high weather resistance.

“Many traditional white paints, although they are designed for durability, but over time, the solar reflectance decreases,” explained another recent paper.

"Materials such as fluoropolymer-based adhesives can increase reflection life, thereby reducing average annual costs."

Creating a single-layer coating that reflects heat directly into space without the need for energy input would be a great victory against the climate crisis, because cooling is usually powered by fossil fuels and has a large overall impact on global warming. 

The new paint needs more testing, but the patent has already been filed. The name has not yet been revealed.

The research was published in Cell Reports Physical Science.