Hey Dan!
well I don't know all the technicalities or specific materials, they are all basically foam. But what I mean with a good quality is one that you can surf serious, big powerful waves and it will last. A performance surf boggie if you will. Brands like Mike Stewart, Pride, Hubbard, VS.
A low quality one on the same wave conditions will bend and/or break in half on a couple of waves/wipeouts. This ones are the ones you would find in Walgreens, Walmart, Kmart, etc. They are mean for a fun time on the beach, not hi performance surfing.
I believe it all has to do with how the foam is expanded. In any case, I figure with a couple of plugs (normally for the leash), you can hook up the clips and give it a go for hunting the pelagic.
At least that what I am trying to investigate.
cheers!