Hi,  I think the material was called Mylar or something like that.
I have always thought that a thin, strong plastic or poly that would
not stretch, or get brittle with age, would make an ideal roll
material.  Hmmm -- transparent rolls ?

Last week I had to resurface a Baldwin tracker bar for an odd reason.
I rebuilt the stack for a customer about seven years ago, and suddenly
the player has developed weak notes, and some notes would fire, but did
not want to turn off.

The old tracker bar had worn to the point that the holes had become
quite sharp.  The bar was stripping the wax from the back of the
paper when played, and the wax had stopped up some of the tracker-bar
tubing, and most of the bleeds!

Cheers.
Andy Taylor