A light/water/fire-stable, cooling wood composite

Passive daytime radiative cooling (PDRC) technology offers a zero-energy route to reducing temperature. Yet, many existing materials rely on petrochemical components or face practical limitations, such as flammability, hydrophilicity, and poor weather resistance. Herein, we developed a sustainable, highly stable radiative cooling wood composite (CWC) by coating a cellulose acetate (CA) binder and nano-silica (SiO2) onto a delignified wood framework. The delignified wood and nano-SiO2 particles of CWC together provide a high solar reflectance of 93%. At the same time, Si-O and C-O-C vibrational modes yield an emissivity of 0.95 in the atmospheric window. Such CWC achieves about 7 °C daytime and ∼10 °C nighttime sub-ambient cooling. In addition, the CA/SiO2 coating endows the CWC with strong weather resistance (solar resistance), hydrophobicity (contact angle of ∼120°), self-cleaning properties, and markedly improved flame retardancy. Overall, this work offers a practical route for designing high-performance, sustainable PDRC materials.