Waterborne polyurethane/cellulose composite aerogel with passive cooling and thermal insulation properties

Abstract Passive cooling is a cooling technology that does not require external energy input, with most passive cooling strategies having high manufacturing difficulty and cost. In this study, we prepared lightweight aerogels (0.093 g/cm 3 ) with high porosity (91.3%), directional pores, enhanced elastic recovery performance, and lower thermal conductivity (0.046 W/mK) through simple mixing, directional freezing, and freeze‐drying. The prepared samples have a reflectance of 87% in the ultraviolet—visible—near‐infrared (UV‐Vis‐NIR) range (0.2–2.5 μm) and an emissivity of 93.6% in the atmospheric transparency window. After covering the box with axial and transverse aerogel samples, the temperature inside the box relative to the uncovered sample box decreased by 12.9 and 13.4°C, respectively. This work provides a feasible method for the research of simply prepared passive cooling materials.