An Intelligent, Recyclable, Biomass Film for Adaptive Day‐Night and Year‐Round Energy Savings.

Passive radiative cooling is a zero‐energy technology vital for mitigating the energy crisis. However, achieving intelligent thermal management across varying weather conditions (day/night and summer/winter) while maintaining sustainability is a significant challenge. Here, a recyclable biomass film engineered for adaptive, year‐round energy conservation is introduced. This film utilizes porous acetyl cellulose (AC) as a cooling‐side matrix, enabling efficient radiative cooling during hot days (8.5 °C reduction) and minimizing overcooling on cold nights (only 2.5 °C reduction). This performance is facilitated by high solar reflectance (96.3%) and broad‐spectrum infrared emission (95.4%), optimizing atmospheric thermal regulation. The reverse side, coated with carbon black (CB), demonstrates superior solar heating (20.9 °C increase), allowing for effortless switching between cooling and heating by flipping the film. Further, the film employs a solvent‐responsive ethyl cellulose (EC) adhesion, ensuring durability, complete recycling, and reuse. With ultraviolet (UV) resistance, self‐cleaning, and durability, coupled with intelligent thermal management, this work provides new ideas for advanced radiative heat management materials, enabling adaptive control during both daytime/nighttime and summer/winter. [ABSTRACT FROM AUTHOR]