: I am doing some experiments for molding a kayak seat and would appreciate
: some input.

: I want to use using expanding polyurethane foam ["Great Stuff"] for
: the core and a thin coat of fiberglass for the skin of the seat.

: The mould is made from burlap and a plaster-like material used for leveling
: floors.

: I was thinking of saturating the mold with paraffin wax as a base and then
: spraying something [Teflon?] on top.

: Any suggestions for a mould release agent?

PVA, or Polyvinyl Alcohol is a great mold release, commonly used for both epoxy- and polyester-based fiberglassing operations. You still need to wax the mold, then brush on the PVA. When it's dry, go for the glassing, then foam. It should pop off the mold easily.

Consider buying an actual marine two-part expanding foam, rather than using the foam in a can, since the former is more water resistant, and the latter can easily get very waterlogged!! For as little volume as you'll be filling, the commercial grade stuff won't cost much more.

For example, US Composites has a 4 lb. kit of 2-lb density foam that will fill 2 cubic feet (probably enough for 4 or 5 seats) for only $15, which would be cheaper and much, much, more durable per seat than the Great Stuff.

: Any other thoughts on keeping the polyurethane foam from gluing the mold
: together?

Keep it away from the edges as much as possible, or hang a strip of masking tape off the edges.

Shawn