A large proportion of thin-gauge containers for the food packaging sector is produced via the thermoforming of extruded thermoplastic sheet (1-4). The production of high quality thermoformed parts is critically dependent on the standard of extruded sheet feedstock used. One method of optimizing the properties of extruded sheet and those of the final thermoformed article is through the incorporation of nucleating agents (5-10). This paper discusses the influence of nucleating agents on the extrusion and thermoforming characteristics of polypropylene. The potential of white titanium dioxide pigment particles as a viable nucleation source for polypropylene is addressed. Evidence is also presented that suggests that nucleating agents may play an important role in controlling the extent of physical change taking place in extruded sheet as a direct result of post-production aging.