Wayne Finger asks about leather for busker organ bellows. I find
that lambskin is a good choice for smaller hand cranked organs.
If you buy skins in the 1 to 2 ounce thickness range, you should
end up with skins roughly .020" to .030" thick.

Before cutting out the leather, seal it by rolling on a coat of
PVC-e glue, thinned 1 to 1 with water, to the grain side of the
skin. A miniature paint roller works well for this. Let dry and
roll on a second coat and let dry. The leather will now be virtually
airtight and ready for use. Lambskin in full skins can be purchased
from https://theleatherguy.org/ 

As a side note, lambskin sealed with PVC-e as mentioned above on
the grain side (not the nap side that seals against the valve seat),
makes an extremely airtight leather for valve facings. Seal the
leather before punching out your facings.

Bruce Newman
Gold Beach, Oregon
https://newmanrestorations.com/