There are multiple variables affecting delam and bonding.
Polystyrene surface energy.
Appropriate adhesives.
XPS minimum Compressive strength (correct foam density).
Lack of XPS porosity – “small” closed cells.
Perforation number, size, shape, orientation, surface area (internal & board surface distribution). Large (relative) circular perforations have low surface area to volume ratios – you want high surface area to volume perforations.
Glassing schedule.
Load and impact dispersion (deck skins: EVA, Cork, etc).
Foam temp (internal gas volume) at time of glassing – core and surface layer – affecting post glassing expansion and contraction. XPS does not out gas (closed cell foam cannot). Which is more likely to cause delamination, expansion or contraction?
Hand oils on the surface of non-porous foam, from handling during shaping and glassing. Wear clean or new dish washing gloves.
Board color – white to reflect solar radiation.
Design and construction must consider these variables.
There are many generalized assumptions when discussing XPS for surfcraft. I am not trying to convince anybody to use XPS. Just offering input to those who do want to try it…