Thermal measurements and optical comparisons of the PDMS film, SiO_2HP, and PSHF_HP. (A), (B) Digital and infrared images of PSHF_HP. (C), (D) Digital and infrared images of PDMS film, the temperature test points of (B) and (D) correspond to the labeling temperatures. (E) Infrared image (blue) of PSHF_HP film and infrared image (reddish yellow) of a caved metal plate on PSHF_HP film. (F), (G) Reflectance and emissivity spectra of the PDMS film, SiO_2HP, and PSHF_HP. (H), (I) Simulated reflectance and emissivity spectra of the porous and nonporous PDMS films. We kept the effective thickness of each model consistent during FDTD simulation (effectively ~100 μm). (J), (K) Spectral refractive index (n) and extinction coefficient (κ) of pristine PDMS film, showing multiple extinction peaks in the LWIR wavelengths and negligible absorptivity in the solar range.