A method of forming a blow moulded container in the form of a tub, the method comprising the steps of: i) providing an injection moulded preform composed of a biaxially-orientable thermoplastic material, the preform being substantially planar, wherein the substantially planar preform has a surface area A of from 5,000 to 50,000 mm 2, wherein the substantially planar preform has a wall thickness T of from 0.3 to 2.5 mm, over at least a central major portion of the preform, and wherein the substantially planar preform has an average bulk width W' and a bulk depth D', the bulk depth D' being at most 25 mm, and the ratio of average bulk width W': bulk depth D', defining a bulk aspect ratio, is at least 5:1; ii) heating the preform; and iii) stretch blow moulding the heated preform within a mould cavity to form a tub having a bottom wall and an annular sidewall having an upper edge, the tub comprising biaxially oriented thermoplastic material in the annular sidewall and at least an outer portion of the bottom wall, the stretch blow moulding step using at least one stretch rod to engage an inner side of the preform and axially to stretch at least a part of the preform prior to blowing a pressurized gas against the inner side which urges the opposite side of the preform radially outwardly against the mould, wherein the tub bottom wall has a surface area of from 3,500 to 40,000 mm 2 and the annular sidewall has a height of from 35 to 150 mm, wherein prior to the stretch blow moulding step iii) the mould cavity is pre-pressurised with a gas, and during the stretch blow moulding step iii), after the preform has been axially stretched by the at least one stretch rod and before blowing of the pressurized gas against the inner side, the pre-pressurised gas applies a resistance force against the opposite side of the preform to cause at least one region of the preform surrounding the stretch rod to bow radially inwardly towards the stretch rod. i) providing an injection moulded preform composed of a biaxially-orientable thermoplastic material, the preform being substantially planar, wherein the substantially planar preform has a surface area A of from 5,000 to 50,000 mm 2, wherein the substantially planar preform has a wall thickness T of from 0.3 to 2.5 mm, over at least a central major portion of the preform, and wherein the substantially planar preform has an average bulk width W' and a bulk depth D', the bulk depth D' being at most 25 mm, and the ratio of average bulk width W': bulk depth D', defining a bulk aspect ratio, is at least 5:1; ii) heating the preform; and iii) stretch blow moulding the heated preform within a mould cavity to form a tub having a bottom wall and an annular sidewall having an upper edge, the tub comprising biaxially oriented thermoplastic material in the annular sidewall and at least an outer portion of the bottom wall, the stretch blow moulding step using at least one stretch rod to engage an inner side of the preform and axially to stretch at least a part of the preform prior to blowing a pressurized gas against the inner side which urges the opposite side of the preform radially outwardly against the mould, wherein the tub bottom wall has a surface area of from 3,500 to 40,000 mm 2 and the annular sidewall has a height of from 35 to 150 mm,