I'll make a guess, but generally speaking when someone refers to fiber glassing a plane they mean fiberglass with either epoxy or polyester resin. The reason is this gives a hard surface, and if done correctly will not add a lot of weight but will give a hard surface for the final finish.

I use either .5oz or .75oz per sq. foot fiberglass and an epoxy finishing resin, sands easy and if you thin it just a tad it will penetrate the surface and give a tough hard finish.

Ron