Preform assembly (1) for blow moulding a container (20), comprising at least a first (2) and a second (3) preform, wherein the first preform (2) is positioned inside the second preform (3) before blow moulding the preforms into the container, wherein each preform has a body forming portion having a wall thickness of less than about 8 millimetres, preferably less than about 6 mm. A container blow moulded from the preform assembly and a method and an apparatus for forming the preform assembly are also disclosed.