Chitosan‐Network Hydrogels With Complementary Radiative Cooling Modes for Sustainable Thermal Management

ABSTRACT Passive radiative cooling (PRC) provides a sustainable solution for building energy management. However, it still remains a huge challenge to fabricate cost‐effective and scalable materials with complementary radiative cooling capabilities. Herein, chitosan (CS)‐based hydrogels were fabricated by adding radiative cooling fillers—barium sulfate (BaSO 4 ), titanium dioxide (TiO 2 ), and silicon dioxide (SiO 2 ) to achieve selective enhancement of either solar reflectance or infrared emissivity. Through optimization of filler type and loading, CS/BaSO 4 and CS/TiO 2 hydrogels exhibit a peak solar reflectance of 87% (0.4–1.0 μm), enabling outdoor sub‐ambient cooling of 7°C under peak solar radiation. The CS/SiO 2 hydrogel (S3‐30) exhibits significantly improved atmospheric window emissivity of 88% (8–13 μm), facilitating efficient nighttime radiative heat dissipation. The imine‐crosslinked CS networks provide excellent solid–liquid dual‐phase stability, preventing water leakage while maintaining facile processability. More importantly, indoor simulations show that temperature is reduced by 2.2°C–4.2°C in model building, while 12‐h outdoor field validation confirms stable sub‐ambient performance. This work proposes a facile, versatile and biopolymer‐based method to fabricate radiative cooling coatings with complementary functionalities, offering a new pathway toward sustainable thermal management in built environments.