Dealing with leaking boards is such a pain and something I would like to avoid in my next custom foam core board.
Fused Cell Foam seems like a good idea. Talked to few builders and it seemed outside of their purview.

Anyone has experience with that and know how to go about getting such a core?

If it is true, I'd also like to have it. Maybe someone like WarDog (of SUP Sports) will chime in and see what he thinks about closed cell foam.

Vacuum bag a thin 1/8 layer of Divinycell ($$$) over some 1# EPS and you got yourself a $700. bullet proof foam blank.

That's how my sailboards were made in the mid 90's on Maui. I always wondered how JP Australia's "Pro" model sups were constructed because they are so light and strong (without using carbon). Well, I fixed a ding on my Pro recently and it looks like it was bagged with Divinycell too.

As I understand, Superfused Molded EPS (call it 'fused cell') is heavier than Block/Slab Cut EPS and probably more expensive. It is also more prone to pressure dings, as is PU foam which is even heavier. The point of Block Cut EPS is reduction of weight with such large boards. Vacuum bag a thin 1/8 layer of Divinycell ($$$) over some 1# EPS and you got yourself a $700. bullet proof foam blank.

TallDude, Could you please explain why Superfused Molded EPS is more prone to pressure dings?  My Slab cut boards pressure ding easily also and they absorb water like a scotch blue kitchen sponge when dinged. Thanks.

Actually the heavier weights of EPS are more waterproof as well. The more air you introduce into the bubbles, the more of them will be broken. If you're happy with a blank that weighs twice as much you can just specify three pound EPS. It adsorbs less than 1 percent water VS 1 pound at 5 percent by volume. I think the biggest value of extruded foam is flex control, but shapers need to learn how to use it. At the volumes of typical SUP boards and XTR blank will probably be pretty heavy, but it might be worth it for some shapes. 1 pound EPS is very heavy with 5 percent water.

I'm not sure what fused cell EPS really is--might just be heavier EPS.

I think in the early days the Extruded foam boards delammed readily because the gasses trapped in the foam during production eventually make their way out of the foam. That might have been solved by now.