: Hi Pedro,

: I don't know what the paddle makers use but I have used this Klegecell in 20
: lb density for rudder fins and helmet mold plugs.

: You may want to poke around this site a bit for some answers.

: http://www.diabgroup.com/aao/a_products/a_prods_3.html

: I have also laminated thin balsa sheets between carbon fiber and that works
: only if stiffened sufficiently. Any flex will equal crushed balsa and
: failure. Worked for a Wing paddle but not for a backrest structure.

: Best,

: Reg

In general you want to use higher density foam in thinner sections, for a paddle I'd want at minimum the 20 lb. density (there are structural foams up to around 100 lb/ft3). As per usual this doesn't apply to every situation

Bill H.