Method of forming an article

A hollow article for use as a beverage cup, or as a container, the hollow article having an annular sidewall and a base wall defining a central hollow cavity, a top rim of the sidewall and a bottom end of the sidewall, wherein the annular sidewall, base wall, top rim and bottom end are an integral moulding and the hollow article is composed of a single thermoplastic material, wherein the annular sidewall extends upwardly away from the base wall and terminates in the top rim and the annular sidewall has a substantially smooth inner circumferential surface, wherein the annular sidewall comprises a plastics material composed of a sandwich structure of inner and outer skins and an expanded cellular foam layer therebetween, wherein the expanded cellular foam layer in the sidewall extends upwardly away from the base wall and comprises an annular array of reinforcing areas extending longitudinally along the sidewall in a direction between the top rim and the bottom end, the reinforcing areas being mutually separated by an annular array of spacer regions extending longitudinally along the sidewall in a direction between the top rim and the bottom end to provide alternating reinforcing areas and spacer regions around the annular sidewall, wherein the reinforcing areas and the spacer regions are between the top rim of the sidewall and the bottom end of the sidewall, wherein the reinforcing areas comprise expanded cellular foam of a first density and the spacer regions comprise expanded cellular foam of a second density, wherein the first density is higher than the second density, wherein the expanded cellular foam in the reinforcing areas of the first density has a more uniform size distribution, and a smaller average size, of cellular voids than the expanded cellular foam of the second density in the spacer regions.