building model aircraft, had an ideal product for recovering bellows. I believe it was called "MonoKote", and was a very thin polimer shrink sheet that was applied with a heat tacking iron.

Don't know if it's still available....but judging from how good it was at it's job, I would guess so. It was available in a rainbow of colors. I've used old scraps to redo an older folder.

Just ran a search and it is still marketed through shops carrying "Top Flite" supplies.