Pvc Pet and Xps foam for Sandwich core

I guys, I would to know your experience about the use of sandwich core for boat building. What do you prefer and why? Please consider only epoxy for resin to avoid solvent reaction with the foam. Anyone have used xps? The only problem is the shear strenght related low density foam? What density do you prefer on bottom, side and deck?

Thanks in advance

 

I have used low density xps, corecell M and pvc corecell, and plascore for hand layup.

The corecell M is pretty special, but costly. The difference between the pvc and M cores are not significant. The M is special for boats used in hot areas.

XPS does not work well. I used it where if it failed it would not matter. The problem is the shear strength of it is jist so poor that bonding requires extra work for a small benefit. I abrade the surface of xps with 36 grit paper. This effectively doubles the surface area (I assume) and then I use a bog coat and it seems to hold a bit better. Avoid it for a hull.

Plascore worked well for me for a catamaran cabin base. The layup is a bit heavy, but I really needed 52" panels and the idea of making 8 of them on the vac table and taping versus laying up twice and flipping won me over. And the plascore I used was 1" thick and 25-35% the cost of corecell M. My project is expensive; so nice to save a buck when I could.

 

Thanks for reply what do you think about the very high price for xps polystyrene foam? It seems like polystyrene edil foam for wall and soil the difference is only for the holes or trapezoidal pattern for resin joint between the skin to increase shear modulus?