In its simplest formula – a single pane of glass 1/8″ reduces heat loss by about 90% vs,.. and open hole or window. For you R-value fanatics, by insulating the glass, we improve the R1 of single glass to a whopping R2 for insulated glass. When we add Low-E coatings, we can get about R3, and when we then add argon gas into the airspace between panes, about R4 is possible.