Researchers at Purdue University have developed an innovative “ultra-white” paint that represents a significant advance in passive cooling technology. Designed to reflect an exceptionally high percentage of incoming sunlight while simultaneously releasing heat in the form of infrared radiation, this paint demonstrates the two essential mechanisms required for effective radiative cooling. The research has attracted global attention for its potential to reduce reliance on energy-intensive air conditioning systems.

The most remarkable result of this work is the paint’s ability to reflect up to 98.1% of sunlight, a figure that surpasses many existing so-called “heat-reflective” white paints. Traditional white coatings typically absorb a non-negligible fraction of solar energy, which can still lead to surface heating. By contrast, the Purdue formulation absorbs so little solar radiation that surfaces coated with it can remain cooler than the surrounding air, even when exposed to direct midday sunlight. This phenomenon, known as below-ambient cooling, is a defining feature of advanced radiative-cooling materials.

Achieving such performance required a departure from conventional paint chemistry. Instead of using titanium dioxide—the most common white pigment in commercial paints—the research team employed a very high concentration of barium sulfate (BaSO₄) particles. Barium sulfate has a wide electronic bandgap, which allows it to reflect more solar radiation while absorbing less ultraviolet light. In addition, the researchers carefully optimized the particle size distribution so that the particles scatter a broad range of wavelengths across the solar spectrum. This multi-scale scattering effect significantly boosts overall reflectance.

Experimental tests and independent coverage of the research showed that the ultra-white paint could cool surfaces several degrees Celsius below the ambient air temperature under strong sunlight. In nighttime conditions, when radiative heat loss to the cold sky is even more effective, the temperature drop was reported to be even greater in some scenarios. These results highlight the paint’s ability to function continuously, unlike conventional cooling methods that require electricity and mechanical systems.

The core findings of this work were published in the peer-reviewed journal ACS Applied Materials & Interfaces, under the study associated with DOI: 10.1021/acsami.1c02368. The paper provides detailed experimental data on the optical properties, thermal performance, and material design of the BaSO₄-based paint and film coatings, establishing a strong scientific foundation for further development and scaling.

From a practical perspective, this technology is often discussed as a promising tool for reducing building cooling demand, particularly in hot and sunny climates. Roofs, exterior walls, and other sun-exposed surfaces coated with ultra-white paint could lower indoor temperatures and reduce the load on air conditioning systems. However, researchers also emphasize that real-world impact depends on multiple factors, including climate conditions, building geometry, insulation quality, and the total surface area coated.

While the paint is not a standalone solution to global cooling challenges, it represents an important step toward energy-efficient, low-cost, and passive climate adaptation strategies. As cities continue to warm and energy consumption rises, innovations like Purdue’s ultra-white paint may play a meaningful role in reducing emissions and improving thermal comfort in the built environment.