A pouch comprising: • a flexible bag having an opening at one end; • a safety valve arranged inside the bag to substantially prevent the content of the bag leaving via the opening, said valve comprising: • a first pair of sheets, each sheet of the first pair of sheets having a proximal end in the vicinity of the opening that is secured to a wall of the bag and a distal end opposite the proximal end along a longitudinal axis (Dl) of the bag; • a second pair of sheets, each sheet in the second pair of sheets extending inside the first pair of sheets and having a proximal end situated in the vicinity of the opening, and a distal end closer to the opening along said longitudinal axis (Dl) than the distal end of the sheets of the first pair of sheets; and • a third pair of sheets, each sheet of the third pair of sheets extending inside the second pair of sheets and having a proximal end in the vicinity of the opening, and a distal end closer to the opening along said longitudinal axis (Dl) than the distal end of the sheets of the second pair of sheets; the pouch being characterized in that: • the sheets of the first pair of sheets and of the second pair of sheets are locally bonded together in the vicinity of the distal end of the sheets of the second pair of sheets, at a plurality of primary bonding points that are spaced apart from one another and that do not bond the sheets of the third pair of sheets with the sheets of the first or the second pairs of sheets; and • the sheets of the first, second, and third pairs of sheets are locally bonded together by a plurality of secondary bonding points that are spaced apart from one another; the distance between the primary bonding points and the distal end of the sheets of the second pair of sheets varies along a transverse axis (Dt) of the bag. • a flexible bag having an opening at one end; • a safety valve arranged inside the bag to substantially prevent the content of the bag leaving via the opening, said valve comprising: • a first pair of sheets, each sheet of the first pair of sheets having a proximal end in the vicinity of the opening that is secured to a wall of the bag and a distal end opposite the proximal end along a longitudinal axis (Dl) of the bag; • a second pair of sheets, each sheet in the second pair of sheets extending inside the first pair of sheets and having a proximal end situated in the vicinity of the opening, and a distal end closer to the opening along said longitudinal axis (Dl) than the distal end of the sheets of the first pair of sheets; and • a third pair of sheets, each sheet of the third pair of sheets extending inside the second pair of sheets and having a proximal end in the vicinity of the opening, and a distal end closer to the opening along said longitudinal axis (Dl) than the distal end of the sheets of the second pair of sheets; • the sheets of the first pair of sheets and of the second pair of sheets are locally bonded together in the vicinity of the distal end of the sheets of the second pair of sheets, at a plurality of primary bonding points that are spaced apart from one another and that do not bond the sheets of the third pair of sheets with the sheets of the first or the second pairs of sheets; and • the sheets of the first, second, and third pairs of sheets are locally bonded together by a plurality of secondary bonding points that are spaced apart from one another;