Scalable Moisture‐Responsive and Light‐Regulating Films for Building Energy Saving and Privacy Protection

Abstract Traditional indoor environment regulation depends on active energy input, raising sustainability concerns under growing energy demands. This underscores the urgent need for passive solutions capable of confronting heat and humidity loads and reducing building energy consumption without compromising occupant comfort. Herein, a moisture‐responsive and light‐regulating (MRLR) film is designed to combine daytime light modulation with nighttime humidity control for building energy saving and privacy protection. Specifically, MRLR films can reduce the humidity from 91.73% to 53.76% within 6 h, while simultaneously achieving the internal temperature drop by 21.1 °C in the daytime. The dehumidification and cooling performance remained nearly consistent over 300 consecutive cycles, confirming their robust operational stability. Moreover, MRLR films are made from low‐cost, environmentally friendly materials with scalable processes and excellent manufacturability. With a fabrication cost of 13.82 $ m −2 and a payback period of 34 days, they offer strong application potential in buildings. Globally, MRLR films can reduce annual building energy consumption by ≈24.57% and mitigate carbon dioxide emissions by ≈18.88 kg (year m 2 ) −1 through passive light‐heat‐humidity management. These promising films represent a scalable and sustainable solution for passive indoor environment regulation and energy saving in the near future.