For almost 30 years deformable die ring systems have been helping moulders save material, achieve critical wall thickness and meet the stringent requirements for automotive components and UN/DOT certified containers. The conventional die is replaced with a flexible die made from a special alloy that is squeezed and stretched into ovality by two or more actuators. The effect is to vary the parison wall thickness radially and in conjunction with the ‘standard’ parison programmer, a much greater degree of wall thickness control can be achieved. This is particularly useful for asymmetric mouldings like automotive fuel tanks. A controller almost identical to a standard parison programmer is used to flex the die through a sequence of shapes which can be a simple ovalisation or complex shapes with a combination of ovalisation and shifting.