Rotational molding is used to mold a hollow part and is a closed molding process. Applications include inflatable play balls, boat bumpers, squeeze toys, and doll bodies. The finished part exterior surface will be a replica of the interior mold surface.
A similar process to achieve a hollow part is slush molding which uses an open mold and produces a hollow part which is open at one end. Applications include automotive parts and models, as well as toy parts.