Q: What qualifies a window as "insulating?"
A: An "insulating" window is simply a window with two panes of glass separated in the frame by about a half-inch of air space. The air space acts as the insulator, retarding thermal transfer through the window. The insulation value can be enhanced by special coatings on one or both panes of glass and thicker air, such as argon or krypton, sealed into the airspace.