> Most fiberglass tapes are "sized" for use with epoxy &
> polyester resins.

> Chances are the guys at your hardware store won't know what you're talking
> about if you ask them about this. What you're looking for though is a
> "volan" (or another epoxy compatable) sizing.

When used in this context, "sizing" refers to the adhesive used in the manufacturing process to hold the glass fibers together during weaving. Volan is compatible with both epoxy and polyester, and is the most common one used in woven fiberglass cloth. Chopped unwoven fiberglass mat on the other hand usually has a sizing soluble in styrene (base component of polyester) but not epoxy. So stay away from unwoven mat and you probably won't have compatibility problems.