A preform for blow moulding to form a container, the preform being formed of a thermoplastic material, the preform comprising a neck finish at an open end of the preform, an elongate body section and a closed end, wherein the body section has elongate, longitudinally extending inner and outer surfaces each centered about a longitudinal axis of the preform, the inner and outer surfaces defining therebetween a wall of the body section, wherein the wall of the body section has at least one locally thickened portion along the body section, the locally thickened portion being thicker than adjacent first and second thinner portions at respective opposite longitudinal ends of the thickened portion, the thickened portion having an inner surface portion which is nearer to the longitudinal axis than respective first and second inner surface portions of the first and second thinner portions.