Spectral plots of thermal radiation emitted by an externally heated polyimide MIM sample with D = 1500 nm diameter discs are given in Fig. . Emitted thermal radiation spectra, shown in Fig. , clearly mirror the reflectance, and by extension absorbance, exhibited by the metasurface. This shows that the plasmon-coupled molecular vibrational modes obey the Kirchhoff's law of thermal radiation. At the condition of strong coupling, and due to a relatively large bandwidth of the plasmon resonance, the absorption (emission) spectrum also became broader than that of the intrinsic vibrational mode absorption in polyimide. However, the 1736 cm -1 (∼ 5.76 µm) mode, subjected to a weak interaction regime, generates a spectrally narrow radiation line with an approximately 90 nm bandwidth. This is a marked improvement over the thermal radiation generated from MIM metasurfaces that typically exhibit a 200-600 nm bandwidth. A brief overview of reported MIM metasurface optical absorption and thermal radiation emittance performance is provided in Fig. of Supporting Information.