Certain old-time manufacturers somehow managed to use striker pneumatic
cloth that, after ninety years, is still like new.  The best chemists
today cannot seem to duplicate it.   My suggestion is to not change it
until it fails noticeably, either by developing unacceptably large
holes to the point where the piano becomes harder to pedal on long note
holes, or the coating is getting stiff.

Aeolian must have had several sources for pneumatic cloth.  Rebuilders
encounter stacks where there are both very soft and very crunchy
pneumatics.  Synthetic plastic materials are still suspect.

There is an Australian rubber cloth carried by Schaff piano with the
tightest fabric weave of any modern cloth, which will prevent tight
folds in the material and retards pin-holes from developing.  How long
the rubber coating will last beyond thirty years is still not known.
The cloth is very nice to work with and seems of the highest quality.

As for bellows cloth for pumps, there is a convertible cloth material
for vintage cars, one side cotton cloth, nylon on the other.  Glue the
cotton side.  I've been using it for over forty years, and it doesn't
get hard or develop holes in it, even in commercial applications, as
in a nickelodeon that is in constant use.  It was developed for outdoor
use, and does even better indoors.

The less we disturb these wonderful machines during their lives,
usually the better off they are.

Thomas Binnall