Save your hands the pain of cutting fiberglass by hand. For the price of a good pair of fiberglass scissors, you can pick up this trick little electric cutter.

This tiny tool looks and feels cheesy, but it works extremely well. It easily cuts all materials up to 24 oz. biaxial fabric (the heaviest on which I have tried it), and will also do several layers at once, depending on the fabric. It's easy to follow cut lines, and is just as easy to use in place as on a workbench.
It comes with a little charger for cordless battery operation, but can also be used with a cord. The battery seems to lose its charge quickly when the tool is stored, but with a fresh charge lasts a long time during actual use.
Item # EC-CUTTER-110 at Jamestown Distributors