Superhydrophobic thermoplastic polyurethane/SiO₂ sponge with dual-layer porous structure for summer radiative cooling and winter thermal insulation

Radiative cooling without using electricity is a green way for air-conditioning. However, most previously reported radiative cooling materials persist in cooling at low temperatures, resulting in added heating demand. This study presents a dual-layer porous superhydrophobic thermoplastic polyurethane/SiO₂ (S-TPU/SiO₂) sponge with a synergistic effect of radiative cooling and heat insulation. The S-TPU/SiO₂ sponge exhibits an average reflectance of 94.5% in the solar band (0.3–2.5 μm), average emissivity of 96.8% in the atmospheric transparent window (8–13 μm), low thermal conductivity of 0.066 W/(mK) and excellent superhydrophobicity with contact angle of 153.4°. During summer, the S-TPU/SiO₂ sponge achieves daytime cooling of up to 12.4 °C, maintaining excellent cooling. While in winter, it provides warming of 0.4 °C at night, effectively mitigating overcooling in cold environment. Additionally, the dual-layer porous structure made the sponge superior to common porous materials in mechanical properties with exceptional resilience, which opens up great potential applications in areas such as outdoor seat cushions and building envelope structures.