http://www.roostersailing.com/merchant2/merchant.mvc?Screen=CTGY&Store_Code=1&Category_Code=nat12s
Interesting - are they working with anyone directly in the Class?
Steve Cockerill re-designed the Graduate main sail plan, which may now have been adopted by their Class assoc too.
Alverbanks use Pentex. Have a look at Graham Cam's mainsail. I am pretty sure that is Pentex.
Pentex - polyethylene 2,6-naphthalate.
Mylar - biaxially-oriented polyethylene tetraphthalate. Threads are stronger.
Polyaramid - kevlar in sails in a laminate with either pentex or mylar. I think that's what Graham uses for a main. Ask Alverbanks.
As for pentex being used as a jib - I would go for a shape-keeping dacron (poylester) sail any time.
But whtever the sail type - get out on the water!!!
Cheers!
Jim.