Fiberglass is the American spelling of fibreglass. Same material: a light, strong stuff made from very thin glass threads pressed together, often set in plastic. People use it for small boats, some sports-car bodies, crash helmets, and surfboards: it is lighter than metal and does not rust. Though actually, English stretches the word. The fluffy pink or yellow stuffing in walls, sold to keep heat in, is also called fiberglass, and that stuffing itches. The hard boat-shell and the fluffy insulation are cousins, not twins. You can also use it as a verb: to fiberglass a boat is to cover it with this material. Tiny bits make your skin itch, so people wear gloves.