An improved chemical mechanical polishing retaining ring. A representative embodiment comprises a base portion made from a wear-resistant plastic material, and an upper portion, or backbone portion, made from a stiffer and more wear resistant material. One of the base or backbone portion is preferably overmolded onto the other. The base portion can be generally defined by a flat pad-contacting surface, an outer surface, and an inner surface. The base portion can additionally include channels extending from the outer surface to the inner surface to facilitate transfer of slurry to and from the substrate to be polished during the process. One or both of the base portion or backbone portion further includes a plurality of circular ribs that serve to create additional bonding surface with the overmolded material. The retaining ring may additionally includes a plurality of bosses with threaded insert holes by which the retaining ring is attached to a chemical mechanical polishing system.