I have double pane windows already, why would I need to change them?

Double pane or “Therma-Pane” windows are not necessarily any more efficient than a single pane window. What makes glass options available today so much more insulating than the double-pane of years past is the coatings that they apply to the glass surfaces and the gases they put in between the panes. Low Emissivity treatments are coatings applied to the glass by applying a micro-thin layer of zinc and silver oxides that reflect heat and insulate much in the same way as an emergency blanket. Gases like argon and krypton are denser than air, and when pumped in between the panes of glass, they insulate by slowing down the loss of heat from conduction.