Garry from Madoc, Ontario sent in the recommendation of locating full-arm veterinary gloves (cost 25 cents from a farm supply store) when working with fiberglass.
You could also cover up with newspaper wrappers or bread wrappers to keep your arms itch free. And disposable work suits are available at most hardware stores.
If you don't get yourself all covered up and you do come out itchy -- take some milk to the shower with you. Rubbing milk into the itchy skin actually stops the itch -- and gives you that milky smooth skin you always wanted . . . .