Archie McQuater asks about a supplier for zephyr.  The best zephyr
I have found is available from Herzog in Germany.  They do three
thicknesses and I have never found any de-lamination and it is totally
airtight.  I can recommend Herzog for this and other leathers.  I used
their thinnest for bird and whistling man bellows.

German:  http://www.lederfachhandel.de/orgelbauleder/ 
English: http://www.lederfachhandel.de/orgelbauleder/leather-for-organbuilders/ 
French:  http://www.lederfachhandel.de/orgelbauleder/cuir-pour-orgues/ 

Nicholas Simons, GB