Abstract: The invention relates to a foldable bag that can be unfolded from an essentially flat initial state into an unfolded final state, provided with at least a first, a second and a third sheet for forming, respectively, a first, a second and a third wall of the foldable bag. The first sheet is joined to the second sheet via the third sheet, which third sheet in the initial state is folded along a fold line, wherein the fold line in the initial state is between the first and the second sheet. The foldable bag furthermore has an opening in the first sheet. The fold line of the third sheet in the initial state extends underneath the opening to form a channel between the first and second sheet past the opening. The invention furthermore relates to a combination of a container and empty bag as well as method for the use thereof, wherein the bag is fixed to the peripheral wall of the container by means of a first and a second fixing.