The present invention relates to a container (1) for preparing of a nutritional composition from a powdered or concentrated liquid nutritional formula base, the container (1) comprising: —liquid inlet means (6) designed to be supplied with liquid from liquid dispensing means (20), —an adaptor (4) being provided with engagement means (2) for connecting the container (1) to matching engagement means (20a) of the liquid dispensing means (20), and —a flexible wall portion (31), connected to the liquid inlet means (6) and at least partially defining a compartment (3) for containing a predefined amount of powdered or concentrated liquid nutritional formula base (5) for the preparation of the nutritional composition (5a) upon hydration with the supplied liquid, wherein the flexible wall portion (31) is expandable in a manner that the volume of the compartment increases from a retracted position to an expanded position allowing a sufficient volume of liquid to be supplied into the compartment (3) through said liquid inlet means (6) for the preparation of the nutritional composition.