Double Pane Window Basics
Double pane windows are simply windows that contain an outer and an inner pane of glass. This differs from the windows of old that were single glazed, meaning they contained only one pane of glass. The single pane version usually had an aluminum frame and, although quite strong, were highly inefficient, offering an R value of 1.
Dual pane windows were developed and manufactured as a more efficient technological advance in the window industries beginning several decades ago. The two panes are part of the insulated glass unit, abbreviated IGU. The IGU is a self-contained, sealed unit that contains the dual pane glass, argon or krypton fills, and a non metallic spacer. Dual pane windows will typically offer an R-value of 2. (Triple pane windows will typically offer an R-value of three.)