The term "fiberglass". That's the name Owens Corning gave it - they made the glass reinforcing. In most countries it's called GRP -- glass reinforced plastic. Polyester resin is the plastic part and the glass is the reinforcing. Like steel rebar in concrete. And yes, you can set glass cloth in epoxy resin but that's not the same as "fiberglass' -- as the term is used in the U.S. Also polyester resin normally doesn't sand, only specially waxed polyester resins do. Stick with epoxy is my recommendation. And do what others have already done like the beautiful wood tug hull that was shown several entries back and that was done in epoxy and very light weight cloth. Epoxy is also resistant to water vapor. That's not the case with fiberglass (which is polyester resin and glass.)