Thermochromic Smart Windows Based on Gel–Sol Switchable Hydrogels with Thermal Stability, Bidirectional Temperature Responsiveness, and UV Shielding Performance

ABSTRACT Thermochromic smart windows hold significant promise for reducing building energy consumption via temperature‐responsive solar regulation. However, conventional systems often suffer from limited thermal stability, insufficient privacy protection, and poor UV shielding. Herein, we report a gel–sol switchable poly(N‐isopropylacrylamide)/gelatin (PNG) hydrogel‐based smart window with outstanding cyclic stability, bidirectional temperature responsiveness, and UV shielding. Leveraging the lower critical solution temperature behavior of poly(N‐isopropylacrylamide) (PNIPAM) and the reversible helix‐to‐coil transition of gelatin, PNG smart windows achieve dual‐mode optical switching with exceptional thermal stability. At elevated temperatures (>30°C), PNIPAM undergoes a gel‐to‐sol transition that renders the window opaque, with a high solar modulation efficiency of 70.4%. At low temperatures (