Unfortunately the density of the blank really defines the board and the ride you end up with. This is the reason why Clark Foam is so sought after. Surf Blanks has been one of the only comparable blanks to Clark Foam.
Believe it or not it truly is a real art form in pouring these blanks. The mix has to be dead accurate and the process of pouring a certain way into the mold has to be right too. There's a handful of guys who travel the globe teaching the correct way to do it.
There's a lot of greener ways and recyclable materials they use to build eco friendly blanks some expensive some cheaper, but its the correct density that's just not there. Sure it makes for new and different ways to build blanks but as of yet they just aren't comparable to the good ol polyurethane pour.