This disclosure relates to the manufacture of sponge rubber spheres, such as spheres (10) used for cleaning tubes internally, and the shapes made thereby. The sponge rubber is initially cut into cubes approximating the shape of the final product. Next the sponge rubber is frozen by means of liquid nitrogen. Then while in the frozen state it is machined to the final shape. This machining could be performed by a centerless grinding technique involving a grinding wheel (41), a regulating wheel (42), and a work rest (43). Additionally, a plurality of shapes may be formed at one time from a single block of sponge rubber (30) as shown in FIG. 2.