I've been reading the postings about this subject and thought I'd put my two
cents in.

Ten years ago I rebuilt an Art Apollo grand.  The pouches were zephir skin
and were eaten by insects.  I ordered several skins from several different
sources and none of it was any good.  It is now usually treated with silicone
or something and hot glue will not stick to it.

I finally used pouch leather and sealed it with carters rubber cement thinned
50/50 with naptha.  I used a small piece of tubing to draw it in and put
several coats until they were sealed then dusted them with talc.  I then
installed lifter discs made from good file folder paper.

The piano is still repeating very fast even at low level after ten years.
Since then I have found some zephir skin of OK quality and use it in
whistlers and singing birds and such using fresh thick shellac as a glue.
 Never make your shellac glue out of old out dated shellac as has been
recommended in the past.  Use new flake its not that expensive.

Even with this new found zephir I would still used leather and seal it even
on a prize piano.