GREAT video of how to for a flanged mold .
i first thought the use of fiberglass to make his edging material was not a good idea, but actually it was brill.
i think we all should be sure to keep some FG and Polyester around for this sort of use.

[YouTube]http://www.youtube.com/watch?feature=endscreen&NR=1&v=gzng9HeGNPE[/YouTube]

CarbonFiberCreations

I've been making flange out of chopped strand matt for years but I must say sign board is cheaper and  nothing bonds to polypropylene making your own costs more and you can't cut with blade,so I recommend sign board.