Considering both the processability and the high reflectance required, we use room-temperature interfacial polymerization to synthesize PANI-CSA in m-cresol as the stock solution. As shown in Fig. , this method features the high molecular weight polymer chain acquired by confining the polymerization growth at the phase boundary between the solid oxidizer and liquid acidic monomer solution , suppressing numbers of polymerization initiation and the unfavorable side reaction. Compared to most other synthesis methods, the resulting PANI-CSA has a much higher crystallinity (Supplementary Figure ). Because of the high crystallinity, the ES state of interfacial polymerized PANI-CSA is intrinsically reflective, which is in stark contrast with most CPs whose conducting form is dominated by loss. This improvement of the CP conductivity is the key to significantly enhance the reflectivity at the low-emissivity state, enabling large emissivity dynamic range in conjunction with active metasurface design. Fig. shows the steps of synthesis. Aniline monomers were first polymerized with CSA and ground ammonium persulfate in chloroform at room temperature. The resulting mixture was washed by water and acetone to extract the PANI-CSA, followed by washing, dedoping, and redoping process in m-cresol to accurately control the doping level. The final product was filtered to reduce the particle size due to aggregation before drop casting or spin coating. ES thin films were obtained by drop casting and drying at 50°C on pristine Si or Au/Si wafer substrate, and the EB films were chemically reduced with ammonium hydroxide surface treatment on ES sample. All the samples used for electrical and optical measurements were prepared by interfacial polymerization. The detailed steps of synthesis and sample preparation are described in Experimental Procedure.