A ball has a wall of elastomeric material defining a cavity. The cavity contains a filling which comprises a plurality of substantially closed cells. The pressure in the cavity is substantially atmospheric pressure. The substantially closed cells fill a peripheral part of the cavity adjoining the inner side of the wall, or the cavity is substantially filled with the substantially closed cells. The substantially closed cells have elastomeric walls. At least some of the substantially closed cells are separate hollow bodies. The hollow bodies are microspheres.