Here we go again.  I am a major techie but I have been burned by
all those previously disqualified products used for pneumatics, etc.
I look at new stuff but I am the one they usually call when they wonder
why their instrument does not work after some new product was used to
rebuild it.  We know that Naugahyde, Perflex, Saran Wrap, Polylon
raincoat material, patent leather, garbage bags, plastic table cloth,
sponge Neoprene and synthetic rubberized cloth products do not work as
covering for bellows, pouches, or valves.

There is one common denominator in all these products and why they are
not usable for pneumatic systems: they do not last.  They each work
beautifully for a few weeks, months or even years, until the synthetic
chemical-based airtight component becomes unstable and exudes oil or
breaks down into flakes and gets sucked down into the pump.

Well, Tyvek has been around since the 'sixties.  I suggest there is
cause for further research.  Find some of the product that was made in
1965 and cover pneumatics with that.  I also notice on the Tyvek web
page that it is designed to pass air and vapor.  I would want to cover
a spring-loaded bellows of some kind and see how long it takes to open
when taped up.  If it passes air one molecule at a time it might work
fine, but it sounds like airtight is not one of its attributes.  In
fact, its ability to pass air is one of its sales points.

If you stay with traditional products but ask our top rebuilders where
the best suppliers are, you will be able to build an instrument that
will last long enough for your grandchildren to be able to enjoy it
without replacing some product used in its manufacture.

D.L. Bullock
http://www.pianoworld.us/