What is usually used for pouches on band organ valve boards or in
valve blocks is tan pouch leather.  It is not particularly cheap, but
I'd recommend spending even a little more money and going for kangaroo
leather.  It is available in various thicknesses from Columbia Organ
Leathers (http://www.columbiaorgan.com/col/) and also from the Leather
Supply House (http://www.leathersupplyhouse.com/default.htm).  Perhaps
in pouch application, there isn't much difference in life span between
the two leathers, but in applications such as small folding pneumatics,
the kangaroo should outlast the tan pouch leather or thin rubber cloth.

Whereas you can tear tan pouch leather with your fingers, it is almost
impossible to tear the kangaroo.  Both types of leather need to be
sealed, because they are so thin that they are very porous.  You will
find ideas about various sealants (e.g. egg white, grease, rubber
cement, flowable silicone) in the MMD archives.  My choice is the
flowable silicone.

Both kinds of leather are easy to glue down, but once you have sealed
the hair side, especially with the silicone, you can't get glue to
stick.  So you have to make provision for that.

Pete Hallock, Agawam, Mass., sent me some Polylon, which I haven't
tried anywhere yet.  You can find more information about that material
in the archives too.  It needs to be glued down with special cement,
but it doesn't need sealing.  The Polylon sample is maroon, the
kangaroo I've seen so far is white, and the tan pouch leather is just
that: tan.

Matthew Caulfield
Irondequoit, New York

P.S.  I see that the Columbia Organ Leather web site says that kangaroo
is not available from them right now.