Container and set of preforms for forming a container

A bag-in-container type container, comprising an inner container and an outer container, wherein a neck region of the bag-in-container type container is provided with at least one opening for introducing a pressure fluid into a space between the outer container and the inner container adjacent thereto, wherein the bag-in-container type container is provided with coupling elements for coupling of a connecting device to the bag-in-container type container for introducing the pressure fluid through said at least one opening into said space between the inner and outer container, wherein the bag-in-container type container comprises a shoulder portion adjacent the neck region, wherein in the shoulder portion the inner container has an outer surface and the outer container has an inner surface, the inner surface and the outer surface facing each other, wherein in at least one of the facing surfaces or between said facing surfaces at least one groove is provided, the groove running along said shoulder portion, wherein the at least one groove is formed between two adjacent ribs formed on the inner surface of at least the shoulder portion of the outer container and/or the outer surface of at least the shoulder portion of the inner container, wherein the at least one groove has a width smaller than the width of the ribs, seen in a circumferential direction of the container.