To understand the design principles behind mid-IR electrochromic devices, it is essential first to examine the fundamental mechanisms of radiative heat transfer and emissivity. The emission of heat as radiation is a fundamental phenomenon for all objects with a temperature above 0 K. For the human body, which behaves nearly as a black body, heat is primarily radiated in the mid-IR (8-14 μm wavelength) range, peaking at approximately 9.5 μm. In indoor environments, radiation accounts for nearly 50% of the human body's heat dissipation .