Biohazard

Question for anyone following this: the reproduction seals for the firewall are made of this thin, white open-cell foam. If you've ever ordered any repro firewall stuff, you know what I'm talking about. Is this some really awesome gasket material or just "correct" for the purists? I'm really considering fabricating some of my own out of a denser, closed-cell type of material for better function - particularly in critical leak areas like the wiper pivot holes.

Input greatly appreciated.