the invention is an integrally blow - moulded bag - in - container obtainable by blow - moulding an injection moulded multi - layer preform . the bag - in - container includes an inner layer forming the bag and an outer layer forming the container , and a single opening , the mouth , fluidly connecting the volume defined by the bag to the atmosphere . the container further includes at least one interface vent fluidly connecting the interface between inner and outer layers to the atmosphere , wherein the bag is anchored to the outer layer at at least one point remote from the single opening and interface vent . the invention also relates to a process and a mould for the production of the blow - moulded bag - in - container .