Injection molded preform and manufacture thereof

An injection moulded thermoplastic preform for blow moulding to form a container, the preform comprising a lower closed base portion, a hollow body portion, a hollow transition portion between the lower closed base portion and the hollow body portion, and an upper open end portion adjacent to an upper part of the hollow body portion, wherein the closed base portion comprises a central part which extends over at least 50% of an internal radius of a lower end of the hollow body portion, the central part having an external surface which comprises an outwardly raised gate part surrounding a central longitudinal axis of the preform and a first peripheral part surrounding the gate part, the first peripheral part being convex and an internal surface which is concave and comprises a middle part opposite the gate part and a second peripheral part surrounding the middle part, wherein the first and second peripheral parts define a first, downwardly and radially inwardly tapering portion therebetween which increases in thickness from a radially outer end of the first tapering portion adjacent to the hollow transition portion to a radially inner end of the first tapering portion adjacent to the gate part and the middle part opposite the gate part, wherein the first peripheral part is curved and has a first radius of curvature and the second peripheral part is curved and has a second radius of curvature, wherein the first radius of curvature is greater than the second radius of curvature, wherein the central part has a radius RCP, measured at the internal surface of the preform at the radially outer end of the first tapering portion and along a direction which is orthogonal to the longitudinal axis of the preform, of from 6 to 8 mm and the first tapering portion increases in thickness δT by from 0.075 to 0.25 mm from the radially outer end of the first tapering portion to the radially inner end of the first tapering portion, wherein the ratio of RCP/δT is from 30 to 70, and the transition portion comprises a second, upwardly and radially outwardly tapering portion extending away from the central part to connect to the hollow body portion, the second tapering portion increasing in thickness from the central part to the hollow body portion.