Guys 

Visiting a boat builder yesterday, who is building a mostly carbon cat for himself for the local regattas and pushing the limits a bit with some bleeding edge materials to reduce weight.  

What was interesting is he's trying out an XPS core from a german company 3D Core.

He is not using it in production yet, will use his boat as a guinea pig first but was happy with the test panels, with a basic workshop (non scientific) test comparison against PVC 60/80. I pressed the foam with my nail and it imprints easily, quite soft.

Seems that, to up the compression strength etc. they create channels "3D honey comb" spaces for the resin to fill, which takes away some of the wight difference. But according to his test panels he's shaved the weight down to about 75% of PVC foam. He's using this for the cabin top only at this point.

Attached is a pic after bagging, with fairing starting.

Data and tests here:

https://3d-core.com/en/products/foam-types.html