Abstract: The invention relates to a deformable flexible pouch for a rigid bottle. The deformable flexible pouch is of the one-piece type, which comprises a rigid upper part (3) comprising an orifice neck (5) and a flexible and deformable lower part (4) and is assigned to means intended for ensuring the dispensing of said products without the return of air into the pouch, the two parts (3, 4) being articulated on one another in such a way that the top of the inner wall of the lower part (4) is laid against the inner wall of the upper part (3) during the shrinkage of the pouch (2). The flexible lower part (4) of the pouch has a contraction (7) forming a concertina having a form such that it is folded back onto the inner wall of the rigid upper part (3) when it shrinks, said contraction (7) being formed in the upper part of the flexible pouch (2). Use for the dispensing of liquid or pasty fluid products.