Thermochromic manganite represents a promising energy-saving material individualizing tunable emittance via external stimuli to manipulate thermal radiation and automatically regulate temperature. However, the ceramics fabricated from the manganite are commonly hard and brittle, which make the fabrication of their flexible device very difficult. Here, large-scale thermochromic foils (TFs) prepared via manganite nanoparticles (NPs) and polyimide (PI) is flexible with thermal emittance self-adjusting from 0.31 to 0.77 upon heating, which the emittance is enhanced by 148%. Especially, the emittance increases dramatically with temperature till 293 K, followed by a leveling off. It is suggested that the PI transparency and the filling ratio of NPs are two important parameters to optimize the thermochromic properties of TFs. Our experiment demonstrated that TFs fabricated with the fluorinated PI can save at least 61% energy consumption versus the existed optical surface mirror at low temperature. The flexible TFs has good prospects for application in smart thermal management.