What is the best type of fiberglass to use for molds E-glass or S-Glass and what is the best type of resin to use with fiberglass for molds.
Thanks guys.
your cloth and resin choices can have a wide influence.
If you’re worked with different resins, you already know what you prefer to work with because of ease of cleanup, ease of wetout, what works best with your laminating style.
What properties you want your mold to have… flexibility? Stiffness? Heat resistance if you’re going to use a hot room??
How quickly you want your molds to set up.
I like to use an epoxy resin, with an 8 hour cure hardner. preference, it’s what i grew up with. If i could find a quick set epoxy that doesn’t heat up alot, i’d use that instead.
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95% of my molds are poly and chopped strand mat. It seems to do the trick for what I need it for.
I just made a mold this weekend from epoxy and chopped strand mat. 2 layers and that thing is a tank. I don’t want the fumes, otherwise, I would have gone poly too. 
Looking for real good Stiffness and that can hold up in the heat or direct sun and will not warped.
Thanks
If I’m using Chopped Strand Mat do I need to do alot of layers for a very stiff mold. Just worried about it warpping in the sun or heat. Thanks
karbon csm is fine… if you want thickness try say… 5 or so layers of 600 will be really thick (after initial layer of 300 or tissue )
if its a flat panel you could try using some coremat or some woven roven…
coremat for a flat surface you think will warp or roven woven for stiffness…
Ideally, the mold and resin should be the same as the final product to maintain the same thermal expansion. This is even more critical if you are using pre-preg.