anatomy of a window :: GLAZING (glass): the (semi)transparent in-fill material... described by # panes... coatings increase energy efficiency... EMISSIVITY: the ability of surface to reflect heat back into a room during cold day, or keep heat outside on hot day (low-E rating is more energy efficient)... SPACER: the space filled with gas(es), sealed to create insulated glazing unit... CONDUCTANCE: measure of how material takes on and transfers temperature... FRAME: enclosing structure