Abstract: The bag (1) includes an elastic band (16) joined to the face (1a) of the bag by two joining areas (17; 2a) in such a manner that the useful length, when the elastic band is at rest (L2), corresponds to the space between the two joining areas on the bag or is less than the length (L1) of the longitudinal edge of the face. The elastic band extends over the entire width of the bag, from one lateral edge to the other, the elastic band being welded to two faces of the bag along these lateral edges, one of the at least two joining areas forming an intermediate joining area (17) located at a distance from the lateral edges.