About the Save Phace Thermal Lens:
Thermal lenses are like a dual pane window. Since the best insulator is air, a dual pane window has two lenses that are attached to each other with a foam or silicon gasket to help prevent fogging. Thermal Lenses do a very god job of this, especially in extremely cold weather or very humid conditions. The down side is you should NEVER submerse them in water or "dip" them in water because if the foam gasket in between the two lenses gets wet, the foam gasket will separate form the lenses and the thermal lens is ruined and they are more expensive.
Alternate Lookup: Dark Smoked Lens