On a number of commercially built packs, I've run into a black adhesive insulation that is pressed over the interconnects. It's generally plastic, but brittle with age.
Does anyone know what this is called, or where I can get some?
You can use a lot of things plastic folder, fiberglass sheet, same sort of rubber paper ect. I have used window blinds. Duct tape has always worked good for wrapping on top.