I’m putzing around with some ideas and need a sanity check. I’d like to install some window insulation along the lines of an insulated panel that recesses into the wall like a pocket door. I was thinking 2”foam board nicely finished that would disappear into the wall when not in use and be able to pull it out at night. Here’s what I’m having trouble with, so check me on it: To simplify things I’m ignoring the studs and other factors, this is for concept only. To do heat loss calculations I take the various R factors for the wall, add them up and multiply them by the square footage. (Example: 3.5” spray foam R-17, 2” foam board R-10 and 3.5” fiberglass R-14 equals R-41. Don't quote me on numbers). Next I would take the window R factor (R-2) and multiply it by the area of the window. (Say 2’x3’=6 sq ft) So far so good. If I slide the foam panel from the wall to the window I’ve removed that insulation from the wall, so now I have a 6 sq ft area that is only R-31 while the 6 sq ft of window goes up to R-12. It seems like there is no gain, but intrinsically I feel there would be a large benefit since I wouldn’t have an R-2 hole sucking the heat out. What am I missing??