Bubble foil is fine for windows that are still used, but is in no way a substitute for real rigid foam insulation.
All this talk of radiant this, and radiant that is snake oil. Just like the paint on insulation's.
There is simply no radiant anything that replaces the real Styrofoam insulation.
I only post this to keep the newbies from thinking they can just line the inside of their bus with reflex, VS real insulation.
"Don't argue with stupid people. They will just drag you down to their level, and beat you up with experience."
Patently waiting for the apocalypses to level the playing field in this physiological game of life commonly known as Civilization