It WORKS and is the perfect solution for door glass. Old windows that never get used should have something to seal the frames as well, but bubble wrap plus shrink to fit does work even better.
"You must be the change you want to see in the world." "First they ignore you, then they laugh at you, then they fight you, then you win." --Mahatma Gandhi
"Preach the Gospel always, and if necessary, use words." --Francis of Assisi.
"Family farms work when the whole family works the farm." -- Adam Klaus
I have done this before- I had access to a load of free bubblewrap- the kind with the big bubbles (smaller would probably be better). I have those upvc-framed windows, they are double glazed but far too big, and they leak a LOT of air around the frames. I didn't take any measurements but I think it helped.