Abstract: A container of blow-moulded oriented thermoplastic material includes a base structure comprising a convex annular surface (which may be divided into a plurality of feet (118) by radial webs (112) and a central re-entrant portion (116). In blow-moulding the container, a moulded preform is enclosed within a mould heated, and stretched such that its bottom surface impinges upon a projecting surface of the mould bottom corresponding to the topmost surface (158) of the re-entrant portion. After blow-moulding, the material of the re-entrant portion (116) remains unoriented and relatively thick in comparison to the material of the remainder of the base. The unoriented material in the base is substantially confined to the re-entrant portion (116) which itself is strengthened by its relatively thick walls and the base thus exhibits improved creep and stress cracking properties.

Abstract: A container of blow-moulded oriented thermoplastic material includes a base structure comprising a convex annular surface (which may be divided into a plurality of feet (118) by radial webs (112) and a central re-entrant portion (116). In blow-moulding the container, a moulded preform is enclosed within a mould heated, and stretched such that its bottom surface impinges upon a projecting surface of the mould bottom corresponding to the topmost surface (158) of the re-entrant portion. After blow-moulding, the material of the re-entrant portion (116) remains unoriented and relatively thick in comparison to the material of the remainder of the base. The unoriented material in the base is substantially confined to the re-entrant portion (116) which itself is strengthened by its relatively thick walls and the base thus exhibits improved creep and stress cracking properties.