Cooling a building without using electricity may seem far‑fetched, but over several years, a research team at the Chinese University of Hong Kong (CUHK) has shown that a coat of paint can provide a surprising amount of cooling. Radiative cooling has been used as an energy-free process that reflects sunlight off surfaces while allowing for releasing their thermal energy into space. However, the main difficulty of implementing such a paint was its affordability.
In 2023, the same CUHK research team that had previously worked on radiative‑cooling paints published ‘Cheaper Radiative Cooling Paint by Milling Larger Glass Bubbles’ in the journal Energy and Buildings, showing that just five minutes of ball milling could raise the solar reflectance of a glass‑bubble based paint from 75.8% to 95.8%. As a result of outdoor tests carried out at noon, the unmilled coating ran about 9.4°C hotter than the surrounding air, while the milled coating's surface temperature stayed comparable to ambient air, effectively eliminating the heat buildup seen in the unmilled version.
