The early attempts at coated nylon cloth weren't too good, as can be seen
in Polylon.  But that ended with the first batch (bright red coating on
white cloth), and from there on, polyurethane coated nylon has been an
excellent pneumatic covering.  It will outwear anything else I know
about, and glues very well with hot hide glue.

I recommend turning the coated side in on pneumatics and air motors.  I
have sent samples to Jacob Utzig of Hudson Industries who makes hot hide
glue to test and evaluate the bond between polyurethane and wood with
hide glue, and the finding was that it is excellent.  There is a letter
to this effect reproduced in The Orchestrion Builder's Manual.

As with everything else, I suggest always making a test first, to assure
yourself that everything is correct, and that there is no mold releaser
or anything coating the material that might ruin the job.

My test of a pneumatic bond is to seal 28 lbs of air pressure in the
pneumatic with an air gun and rubber cork.  Leaks or poor bonds show up
with a pop and a whoosh!  A good tight pneumatic holds it.  Vacuum
doesn't test the bonds on a pneumatic.  It even seals what would
otherwise be a leak sometimes.  I have also seen covers that almost fell
off by themselves, except for a well-glued open end, and worked pretty
good as a vacuum pneumatic until they were discovered.

Craig Brougher