Radiative cooling works by emitting thermal infrared through the atmospheric transparency window — the 8-13 micrometer band where Earth's atmosphere is relatively transparent to outgoing radiation. In dry climates, this works beautifully. In humid tropical climates, atmospheric moisture absorbs infrared radiation in that window, blocking the cooling pathway. Most of the world's cooling demand is in precisely these humid regions.
A cementitious paint simultaneously radiates heat and evaporates absorbed water, achieving effective cooling even in Singapore's tropical humidity. The paint retains approximately 30% water by mass, self-replenishes from ambient moisture, and maintains 88-92% solar reflectance whether wet or dry.
The dual mechanism rescues radiative cooling for the climates that need it most. When humidity blocks the infrared window, evaporative cooling compensates. When humidity drops, radiative emission strengthens. The paint adapts passively to whichever pathway is available.
The solution to too much moisture in the environment was not to fight it but to make the material sweat. Previous radiative cooling coatings treated humidity as the enemy — an obstacle to infrared emission. This coating treats it as a second working fluid. The same water vapor that blocks the infrared window becomes, once absorbed and re-evaporated, a cooling mechanism in its own right.
The building's skin does what animal skin has always done: sweat when it's humid, radiate when it's dry.