Cool Kitchen: Processing Starch and Eggshell Powder into Sustainable Coatings for Passive Daytime Cooling

Abstract Increasingly frequent and severe heat waves pose a significant threat to human health, intensifying the demand for cooling solutions. Conventional air conditioning offers relief but escalates energy consumption and CO ₂ emissions, exacerbating global warming. Here, a passive daytime cooling composite made from kitchen‐sourced materials, providing a zero‐energy cooling technology accessible to everyone, is introduced. Composed of starch and finely ground eggshell powder, this eco‐friendly composite demonstrates an average solar reflectance of 0.91 and thermal emissivity of 0.95. Applied to concrete, it achieves a temperature reduction of approximately 15 °C compared to uncoated concrete under 800 W m ^{− 2} solar irradiation. With universally accessible ingredients and a simple fabrication process, this cooling composite provides a viable solution for households with limited infrastructure to tackle the growing threat of heat waves.