I don't know about Depron. For use with epoxy-fiberglass laminate the sheet should have good strenght against compression, good epoxy bonding and resistance against delamination. I used commercial foam which was made for core material in laminates. Some pics here;
http://s378.photobucket.com/albums/oo221/Toni_Vakiparta/l_9726/

: I was wondering whether Depron could be used as a core for a kayak. I'd
: thought about backing the sheets with 1oz glass for improved rigidity,
: then cutting it to use for stripping - although hopefully it might be able
: to be used in wider sections and be shaped to follow the forms? Since it's
: closed cell it shouldn't absorb water either. It's used in model aircraft
: construction for it's lightness, although that isn't in itself a factor
: for me, as I'd have to use more glass - Obviously it doesn't have the same
: strength as wood strips, but it does have the advantage that it is
: available to me, whereas cedar isn't in the UK, and I don't have to tools
: at the moment to start milling strips...

: I'd initially thought about using it instead of ply for a S&G - but there's
: no real advantage to that, what I was really wondering was whether it
: could be formed around a stripper to improve the build time.