With respect to Skip Downing's idea that someone used Corfam for valve
facings, Corfam was the DuPont Company's invention of an artificial
leather.  See https://en.wikipedia.org/wiki/Artificial_leather 

My dad was peripherally involved in the making of this stuff in the
1960s.  We had quantities of the early production raw material which
I used to cover large speaker cabinets and, of perhaps more interest
to this crowd, I used a scrap to make a replacement leather belt for
my Edison cylinder record player.  55 years later, that belt is still
functional.

I had early, sample Corfam shoes which were pretty terrible; they
never 'broke in' and they could not tolerate the salty melt water that
I walked in all winter in Montreal in the late '60s.  DuPont sold that
business in the early 1970s.  It's hard to imagine that the U.S. Air
Force was still issuing Corfam shoes in 1981!

Doug Heckrotte