Asymmetric Radiative Cooling Film for Energy-Efficient Thermal Management in Outdoor Low-Temperature Spaces

Mitigating heat stress requires energy-efficient outdoor cooling strategies. Passive daytime radiative cooling (PDRC) has emerged as a promising energy-free cooling strategy, yet its application in outdoor low-temperature spaces remains limited because conventional isotropic designs simultaneously radiate heat to outer space and the protected space. Here, we report an asymmetric radiative cooling film (ARCF) that enables energy-efficient thermal management in outdoor low-temperature spaces through directional thermal radiation regulation. The ARCF employs a bilayer architecture that decouples the radiative functions of two surfaces, combining a polytetrafluoroethylene/silicon dioxide fibrous layer for upward radiative cooling with a low-emissivity aluminum layer for suppressing downward radiative heat transfer. Consequently, the ARCF reduces radiative heat gain into enclosed spaces while maintaining efficient subambient surface cooling. Outdoor experiments demonstrate effective low-temperature preservation, with a maximum chamber temperature difference of 7.2 °C compared with conventional PDRC materials. EnergyPlus simulations further demonstrate substantial cooling energy savings across multiple climate zones. This work establishes an asymmetric radiative strategy for energy-efficient thermal management of outdoor low-temperature applications.