Thermal performance of a window unit is measured using a U-Value which is similar to the R-Values most people are familiar with. Technically speaking, R-Values are normally used to measure the insulating value of a homogeneous material (like fiberglass insulation) rather than a finished component like a window. That’s where U-value comes in. Mathematically, it is the reciprocal of R-Value, and it is normally used to measure the insulating quality of a mixed material installation like a window.
Testing of a single pane “prime” window plus an InnerG window yields a U-value of 0.44. Lower U-values mean better insulating performance. Here’s a chart showing how the InnerG window fares relatively speaking:
Window U-Values from single pane to triple panes
So, the InnerG window makes the poorest quality single pane window (like the windows found in most older properties) into something better than a good quality modern double glazed wood window for much less cost. Additionally, much higher performance can be expected with the InnerG window installed over a better prime window. Don’t replace your old windows, it is much cheaper to insulate them with the InnerG window.
If you want a more detailed discussion of the thermal performance of Acrylic Windows vs Glass windows, there is a detailed technical document about insulating at this link. (30Kb pdf file).