Double Pane Windows
Nearly all windows manufactured today are double paned. The reason is that they are so much more energy efficient than the single pane windows from decades past. Double pane windows are part of what's called an insulated glass unit or IGU. The IGU fits inside the windowframe and contains the two panes of glass, the space between the glass that greatly reduces the noise (see our page on soundproof windows cost for more), the gas fills and the spacer. Together, they are the most important part of making a replacement window energy efficient.
