Windows made of insulated glass have something other than a single pane of glass separating one side of the window from the other. They are considered essential in any serious effort to make a home or building as energy efficient as possible. There are a number of different strategies used for insulated glass in order to make it as effective as possible.

The first thing one should ask about when looking at insulated glass is the R-value. This value shows how prone the window is to losing heat. A window with an R-value of 1 is considered very inefficient. Most insulating glass units have an R-value of 2 or higher.