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Insulated or double glass is constructed of two panes of glass set apart to allow airspace in between. This airspace acts as a buffer which obstructs the transfer of heat from one side of the glass to the other, sometimes cutting the energy loss in half. The two pieces of glass are separated by a low-conductivity spacer that creates the airspace. Incorporated into the spacer is a desiccant system. Desiccant is a drying agent which drastically reduces the moisture between the two pieces of glass after they are sealed together. One can improve overall efficiency even more by applying a Low-E, or low emissivity, metallic coating onto the inner surface of the outer pane. This will allow the window to reflect ultraviolet and infrared rays, while decreasing solar heat gain. This can decrease energy loss by up to 30 percent. The airspace can also be filled with argon, which is a relatively inexpensive gas that increases overall insulation. It is critical that these two pieces of glass are properly sealed around the perimeter of the glass unit. If poor or improperly sealed, the seal can break, allowing moisture and dirt to enter the space between the two pieces of glass. While failed insulating glass still has some insulating characteristics, it fills with condensation and dirt, making it unattractive and difficult to see through. While some companies claim that they are able to repair a failed unit in place, it is better to replace the entire glass unit, or in many cases, the window itself. 2. What is insulated or double glass? < back to list of questions about glass WINDOW GLASS