john,
although i can't answer your question about the foam, i can identify w/ you with people asking questions. i was wet sanding my final epoxy coat( in the drive way) before paint the other day. some guy rolled up and hopped out and started to ask questions about my boat. where i got the plans, what is it made out of, do you paddle, or row like the notre dame sculling team etc. etc...really wierd. i've never seen this guy before. he talked to me for 1/2 an hour or better. my kids were freaked out by the guy, and my wife came outside after he left and asked who my friend was. i had to explain to her i had no idea. it was wierd...yet, kinda' neat. it made me feel good about how my kayak is turning out. stranger still...all of my friends think i'm nuts for building this. well, maybe i am.
take care, and good luck with your foam question.
brett the hitman hart