A raft is any flat floating structure for travel over water. It is the most basic of boat esign, characterized by the absence of a hull. Instead, rafts are kept afloat using any combination of buoyant materials such as wood, sealed barrels, or inflated air chambers. Traditional or primitive rafts are constructed of wood or reeds. Modern rafts may also use pontoons, drums, or extruded polystyrene blocks. Inflatable rafts use durable, multi-layered rubberized fabrics. Depending on its use and size, it may have a superstructure, masts, or rudders.