I have an approximately 7' wide, 7' tall hole in the wall of my apartment, affectionately called a patio door.
It just so happens to have an R-value of near 0. The building is slightly crooked, and the upper portion of the door does not close in the track, rather I have about 1/8" of visibility to the outside where there should be none.
And obviously I've tried sealing this, but I don't know how much good it's doing. I've used the tape-up plastic, but it still seems to want to stay below 50F on that side of the room, and I'm using an insane amount of power trying to keep just this room warm.
Which got me to thinking. I can take as much scrap cardboard from work as I want. Am I thinking correctly, that a few layers, perhaps 4-5 of double-wall cardboard might provide some decent insulation? Is the R-value of cardboard significant enough for this?