I need to add about a half an inch of material to a fiberglass valance and need to know what I can use to hold it's shape that won't stick to the resin.

Aluminum foil, wax paper?

Any ideas?

aluminum foil is good, but some will stick to the resin.
No big deal though as you can easily sand it off.

I've used foil in surfboard repairing without major issues.... could be a better way though.
Like mold releasing agent?

carnauba wax - car wax

Allan,
You can use dam near any material for this that works for the structure.

You have a myriad of choices as far as keeping the resin from sticking.

1) Mold release. Available at any glass supply house and ALL boat shops.

2) Cling wrap. Go steal some from the wifes kitchen.

3) Trash bags. Black being the best for some reason.

4) Car wax.. Put it on heavy. At least several coats. If the surface is porous. Use multiple coats until the surface is like a babys buy. (Not yours)

5) Diesel. (Only good for BIG areas that don't need to be perfect.)

6) "Pam" anti stick spray that you use for frying pans works. It is not good for porous molds. Just very smooth molds.

7) Aarons toe sweat. NOTHING sticks to it.. Just ask his socks......

Cheers,
Clayton

Got it done.

Just waxed some foil and it peeled off like pancakes on a teflon skillet...