My chemistry isn't good enough to expain the difference between PVC foam and Corecell (SAN foam). The advantage of corecell is basically that it has higher elongation to failure figures which means it will withstand impacts and damage better. It also can be very easily heat shaped allowing for a closer fit to the hull and therefore less resin or bog in the structure. Given all F18s are heavy the only real advantage with corecell is its "ruggedness" A brand new boat with PVC or SAN foams will be very similar. But if you're looking at 5 year old second hand boats in 4 years time the odds are the Shockwave will be in better nick. In the early 90s when the F18 rule was written SAN foams where more much expensive, this it less so these days. As I stated above there is no reason to kick the corecell boats out of the fleet. Just make sure no more are built.