A novel fluorine-free water-based passive daytime radiative cooling paint for building roof applications

Passive daytime radiative cooling (PDRC) represents a passive cooling solution for buildings, enabling heat dissipation to outer space through the atmospheric window. For the widespread implementation of PDRC technologies in buildings, scalable and environment-friendly PDRC paints are particularly advantageous and practical, as they can be easily sprayed or brushed onto building surfaces. However, a PDRC paint without VOC emissions and fluoropolymer usage remains unexplored. Here, we developed a fluorine-free water-based PDRC paint by introducing Al 2 O 3 , BaSO 4 , and SiO 2 particles, and glass bubbles into a pure acrylic emulsion. The agitation-based synthetic method is straightforward, and scalable through all room-temperature processing. The developed PDRC paint exhibits a solar reflectance of 0.92 and an average broadband infrared emissivity of 0.96. Continuous 72-hour experiments were conducted in Sydney, which is characterized by extreme heat with a maximum solar irradiance of over 1000 W/m 2 . Our PDRC paint has been demonstrated to be able to achieve a surface temperature drop of up to 6℃ in the daytime, compared to commercial white paint, without sealing it from convection. Furthermore, building energy simulations showed that our PDRC can provide up to 63,000 kWh and 5,000 kWh in annual energy savings for prototype commercial and residential buildings.