A method of producing a container for retaining fluid, the method comprises the steps of: • providing a blank (10) which, when assembled, forms a container; • folding the blank along one or more fold lines across the blank's width to form a substantially rectangular side wall (11) such that first and second ends (23, 26) of the substantially rectangular side wall are brought into close proximity; • sealing the first and second ends (23, 26) of the substantially rectangular side wall to one another; • deforming one or more deformable portions (29, 30) which span across the one or more fold lines such that the deformable portions (29, 30) are disposed inwardly in order to force the remainder of the side wall outwards to create an opening within the blank; and • sealing a base (27) around the circumference of a first edge (14, 20, 22) of the side wall.
