I routinely use Bilon on pneumatics and wind motors.  I service pianos
that were rebuilt with Bilon forty years ago, and the pneumatics are
still airtight.  Granted, the early Bilon, purple with gray backing,
seems to break down.

There was a period when Bilon was not available; so I used rubber-
coated cloth.  After five or so years, pinholes appeared in the folds.
If someone could guarantee rubber-coated cloth of the quality of early
Kimball or Aeolian cloth, I would certainly use it.  But as far as I
know, it doesn't exist; so I use Schaff Piano Company's #668 nylon
sheeting coated with polyurethane.

If I have a restoration job where I feel the customer might want to
keep the system as original as possible, I will give him a choice of
the original rubber-coated cloth that will last perhaps ten years or
Bilon that will last forty years.  As of yet, no one has chosen rubber-
coated cloth.

Don Barton
Barton Player Piano Co.
Minneapolis, MN