|I think you should compare the results to some other core material(like wood to start with if you don't have any other foam), because otherwise the results becomes a bit arbitrary.

>> Peel strength is not really an issue in a sandwich construction.

If the strength of a composite sandwich does not depend on peel strength, why are we measuring peel strength?

Is it just fun?

|What is your reply to Rick W's post from third of May: "I made a long slender prototype hull from a block of XPS."

As noted there, Rick has no idea what the compressive strength of the core was. Assuming Rick did the composite under vac, the 15psi XPS(cheapest XPS insulation) was already compromised. Also note that no other source has suggested water harms the XPS fiber bond. Rob Denny stated he only had delamination in wet layup XPS skiffs where they were walked on. Also note that the cheap 'sawfish' (youtube) XPS kayak/boats are just cheap random XPS and wood glue and polyester bedsheets as skins, have been used for nearly a decade and no delamination noted. Also Rutan planes.

So the idea that water destroys the cheap XPS laminate interface is contradicted by solid data.

Also, can we clarify what grade of XPS we are talking about. Generally there are 2 grades commonly available in the US. The 15psi grade is entirely unacceptable in laminates, IMHO. The 25psi grade is marginal at best, but seems to have been used in many hobbyist projects. Its 170% stronger than the 15psi stuff. The densities are nearly identical, so we can't just call it 2 pound sq foot XPS.

The 40, 60 and 100psi grades are a very different animal. Please don't confuse them.