Biodegradable Paints for Daytime Radiative Cooling

Abstract Radiative cooling technologies help alleviate global warming and the urban heat island effect by reducing the energy load of conventional air conditioning. However, most radiative cooling materials contain nonbiodegradable components that decompose into microplastics and threaten the environment. To address this issue, this work develops a biodegradable radiative cooling paint, experimentally demonstrated to maintain an average surface temperature of 2–3 °C below ambient temperature and around 5 °C below commercial white paint under high solar irradiation (>800 W m–2). Fabricated samples showed a high solar reflectance of 96.6% and sky window emissivity of 0.938. The binder demonstrated complete biodegradation within 3 months in a compost environment. TRNSYS simulation shows high energy savings across the US, with over 400 kWh of electricity saved in hot and dry climates such as Phoenix, AZ. With high UV resistance, mechanical durability, and self-cleaning capabilities, the biodegradable radiative cooling paint is suitable for large-scale deployment.