Fiberglass boat hulls are normally made in a mold, so that the height, width and length of the hulls of boats of a single design all match the original plans. The hull is usually made in four basic steps. The interior part of the mold is covered with a gel coating after which the mold is selected, which is allowed to dry and becomes the shiny surface of the hull. The fiberglass that comes in rolls, like attic insulation or gauze bandage, is laid down and the resin is applied to it before it is put into the mold. Several layers of fiberglass are added one layer at a time, in which sometimes, a core of foam or balsa wood is added before the final layers of fiberglass are laid down, for extra flotation and safety.