Polymer coating cools down buildings. Engineers have invented a high-performance exterior PDRC polymer coating with nano-to-microscale air voids that acts as a spontaneous air cooler and can be fabricated, dyed, and applied like paint on rooftops, buildings, water tanks, vehicles, even spacecraft -- anything that can be painted. They used a solution-based phase-inversion technique that gives the polymer a porous foam-like structure. Source 3b.