I would also second the motion that there is quality fine grain,
bun-cut, long-lasting neoprene sponge material out there, as Robert
Taylor said.  For 88-note players, it's just fine, as long as you know
what to look for, and how to use it, and IF you don't have a decent
grade of leather that would work better.

However, just a warning, regarding building _reproducer valves_ out
of it: neoprene should not make your piano "tighter."  Good quality
leather, as selected in ways that I have formerly suggested, is better
than any neoprene sponge, generally speaking.  Leakage from new,
properly selected leather is so slight, that your pump can easily
handle the total leakage without loosing vacuum.  That should not be
a point.

Leather is able to self-adjust and seal on the valve plate better than
neoprene because it doesn't have as much tack, or surface friction, at
light pressure, and quality leather is always tighter on the majority
of wood seats than neoprene will be.

All valves rise crooked.  That valve must seat quickly when it arrives,
but at an angle, the percentage of seating instantly is less likely
because the edge of the neoprene (being flat and homogeneous) depresses
wherever it touches first and creates a false seat, slightly slowing
the valve surface from contacting quite as quickly, at times.  Another
reason is that neoprene cannot be properly set for valve travel in
Ampicos because of the "cush" or dimensional instability,
thickness-wise.

Depending on the density of the material, which varies from batch to
batch, as the pressure of vacuum rises, it compresses proportionally on
the outside plate.  So if your initial travel is set to, say .035",
then a .010" extra compression of a .0625" thick sponge isn't unusual,
being only about 15% (and that depends on the contact area of the valve
plate).

But that equates to 30% increase in the gap!  That, in turn is
noticeable to a musician.  Granted, to some ears it becomes just
phenomenal -- how much "expression" the piano seems to have!  However,
it is false, melodramatic expression.  "Good" expression is when you
are able to hear sensitive nuances throughout the dynamic range, and
even into the loud passages.

Another feature of neoprene sponge is the fact that it isn't all the
same density.  That means, what worked well for Robert Taylor might not
work equally well for you!  Bob is very experienced and would know if
something wasn't right, but the majority of those who would undertake
to rebuild their pianos would not, until they had rebuilt about as
many.  That experience isn't cheap, and it cannot be taken for granted.
So while he could adjust Ampico valves to work "fairly well"  with
neoprene, I don't believe that many could.

Another factor about using neoprene: never use it in the Duo-Art!
That is one reproducer that will absolutely NOT WORK if it has
perfectly airtight valves.  The reason for this is its regulation knife
valves, which also tend to be airtight.  Very briefly, you establish a
vacuum chamber that cannot leak down quickly enough, and will slam
notes that were supposed to be played softly.  And, there is no
regulating it out.  The Duo-Art relies strictly on the roll for
everything, so it assumes a certain percentage of leak through its
valves at all times, graduating tighter as the vacuum progresses
upward, so the percentage of leakage becomes less.

Finally, neoprene sponge valves eventually take a "seat."  When pounded
by the reproducer, over the course of years, they take a set, meaning,
they become thinner where they are seating.  Now with some rebuilders
who set valves too close, that works out just fine.  But for someone
who knows better, if their valves are changing with use, they should
realize that.

This is a caution that everybody should know about and should think
twice about, before substituting sponge rubber for quality calf
leather.  However, there are many leathers available today (like
car-seat leathers) whose suede is too rough to use for valves.  If
the suede isn't equal to suede jacket leather, I suggest not using it
for valves.  But I do not suggest you then go out and buy some neoprene
sponge, either.

Regardless, neoprene sponge works best on certain 88-note players, like
the Standard Action, when you cannot find suitably stiff and smooth
corrected calf inside valve leather.  In that case, I recommend 1/16"
Craft Foam, available at hobby stores like Hobby Lobby.  And -- just in
case -- you can spray the sheet with dry (high viscosity) electronics
silicone spray before you cut it out.  I strongly suggest not to use
neoprene rubber sponge in reproducers because of the high vacuum
pressures, speed, and precision required!

Craig Brougher