Lorna this is great info, and it does work. Whether it is a temp fix before you can get 'the real thing', or a way to save on your energy costs, or a fix to a rental property- it really works well!
I have been using bubble wrap for years in drafty rental houses and apartments. The house I currently live in is very poorly insulated, and has original double hung windows with wall weights from pre-1940. Some have storms. Some don't. I got a giant roll (30"? Wide) and double-wrapped all my windows. It made a 10*F improvement with the same settings and outside temp. I label and re-use my wrap from year to year.
This year, facing weeks of below 0*F, and once getting to -31*F, I added 'curtains' of plain old fleece from a fabric store that I picked up for $3/yd which was 5' wide. These windows are warmer to the touch than the solid walls now. Gotta love thermal breaks! I keep the curtains down on my Northern/shaded windows, and open the sunny-side curtains to let in the light.
If there is a storm window, I put one sheet of bubble wrap in between the storm and the interior glass, with the bubble surface to outside glass to make more air barriers- including the one between the flat side and the inside glass. Then I make a sheet big enough to cover the entire window frame (using clear packing tape) and attach it with whatever method works best for that window. I've used tacks, painters tape, removable tabs (command-style), tension rods, magnets, etc. my windows went from ice covered and able to blow a candle flame, to no draft with no frost on the inside overnight.
I've also made indoor 'door curtains' for doors I don't usually use in winter, and wrapped my storm doors with bubble wrap too.(with a window flap if necessary
I've also used a layer or two on outside walls under cabinets with susceptible plumbing. My cheap $1 thermometer registered a 20* difference in one cabinet this year when I double lined the base and up the sides and back. Those pipes didn't freeze up this year! Yay!