Multiscale architecturing of high-performance passive daytime radiative cooling cementitious composite

High energy consumption in buildings is increasingly driven by the demand for electrical cooling, particularly in urban areas affected by the urban heat island (UHI) effect. This phenomenon, exacerbated by conventional construction materials like concrete that absorb and retain heat, increases cooling loads and strains energy systems. Energy-free passive daytime radiative cooling (PDRC) technology presents an appealing solution by reflecting solar radiation and emitting heat into the cold universe, with recent polymer composite designs demonstrating potential for achieving high PDRC performances. However, the integration of high-performance PDRC polymer materials in building applications is challenging, primarily due to inadequate mechanical strength and compatibility with construction materials. Here, we combine a cement-based honeycomb architecture with nano-engineered porous polymer to obtain lightweight PDRC-cement composites that deliver both efficient energy-free cooling performance and high mechanical strength. Specifically, the innovative material design achieves excellent solar reflectance (94.9%) and high longwave infrared emission (97.0%), enabling sub-ambient temperature reduction of ∼9.6 °C and a measured net cooling power of ∼196.8 W/m 2 at midday under an ambient air temperature of ∼65 °C – significantly outperforming state-of-the-art radiative cooling construction materials while maintaining high specific compressive strength (0.013 MPa·m 3 /kg). With potential for incorporation into energy-efficient building envelopes, this design approach presents a promising strategy for effective building energy savings and heat island mitigation.