A method of manufacturing a foldable bag for use in a bag-in-box assembly is described. The foldable bag being manufactured according to this method has a folded condition in which it includes at least an inwardly creased bag portion in a longitudinal direction thereof. Furthermore, the bag includes a bottom edge and a top edge opposite to each other in a longitudinal direction of the bag. The inwardly creased bag portion has a first closed end and a second closed end opposite to each other in the longitudinal direction of it. The first and/or second closed end of the inwardly creased bag portion is a free end. The bag according to the invention has an improved unfolding process during filling it, and has such a configuration that it does not cause material stress in certain welded seams such as in known bags.