Supercritical CO2-foamed polyimide/SiO2 nanoporous film for transparent radiative cooling and thermal insulation in extreme environments.

Transparent thermal management films must combine high visible-light (VIS) transmittance, ultraviolet (UV) shielding, low thermal conductivity, and high mid-infrared (MIR) emissivity. Here, molecular design was combined with SiO2-assisted heterogeneous nucleation during supercritical carbon dioxide (ScCO2) foaming to fabricate a nanoporous fluorinated polyimide (PI) film. The optimized foamed film (FP6S1) exhibits an average pore diameter of 71.8 nm, a VIS transmittance of 77.9%, UV blocking above 99.6%, an emissivity of 91.2% over 8-13 μm, and a thermal conductivity of 52 mW m-1 K-1. The nanoporous structure increases the tortuosity of solid heat-transfer pathways and restricts gas-phase conduction through nanoscale confinement while retaining optical transparency and flexibility. During a three-day outdoor test, the FP6S1-covered cavity remained 5.17 ± 0.25 °C cooler than the glass-covered cavity during daytime. Under idealized lunar boundary conditions, the FP6S1-integrated window reduced the simulated cabin temperature by approximately 3.5 °C after 24 h relative to the baseline window. These results provide a route to flexible transparent films that combine UV protection, thermal insulation, and passive temperature regulation.