Insulated or insulating glass is your first line of defense if high energy bills are plaguing your home. Insulated glass consists of two or more panes of glass separated by spacers made of metal or structural foam. This creates an area between the glass panes.
This area is sometimes filled with compressed air, although there may also be a noble gas, such as argon or krypton. This gas traps heat either on its way into or out of your building, keeping the inside temperature closer to what you want it to be.