How Does Therma-Foil Insulation Work? Therma-Foil insulation resists radiant heat flow due to its high reflectivity and low emissivity (ability to reflect and re-radiate heat). It works by reducing radiant heat transfer, as a result of the emissivity of the foil facing. Therma-Foil is a Radiant barrier and will therefore reflect radiant energy. There is…