Double glazed windows are constructed by placing two panes of glass closely together, as opposed to just a single pane of glass. One pane of glass is on the exterior, and one sits securely inside. Between the panes, there is a thin gap that is often filled with argon gas. Argon gas is used to slow the transfer of heat through windows. Since it is so vicious, it acts as a fantastic thermal barrier. Since molecular movement is so restricted within argon gas, far less heat is transferred and far less heat loss occurs. This helps to really improve the energy efficiency of homes.