A method for making a flat bottom bag with a valve, the method comprising steps of: a. overlapping and sealing two longitudinal edges (11a and 11b) of a web to form a continuous tube; b. cutting-off the continuous tube into tube pieces in accordance with desired bag length, wherein each tube piece has at least a first open end and a second open end; c. forming a first pair of flaps (F1, F2) and a second pair of flaps (F3, F4) on the first open end and the second open end, respectively, by folding the ends (18, 22) of the tube vertically, spreading the mouth of the folded open-ends (18, 22) of the tube, and flattening the mouths of the folded open-ends (18, 22) of the tube to form the first pair of flaps (F1, F2) on the first open-end and the second pair of flaps (F3, F4) on the second open-end; d. providing a valve on the second pair of flaps (F3, F4) on the second open end, wherein the step of providing the valve further includes: sealing a cut laminate piece to the second pair of flaps (F3, F4) of the second open end, wherein the cut laminate piece is protruding out of the edge of the second open end of the tube by a predefined offset distance (Do), wherein a mouth distance (Dm) from the longitudinal side of the flattened tube on the second open end is zero so that the valve does not protrude out of the longitudinal side of the flattened tube; and folding the cut laminate piece to form the valve; e. folding and flattening both the pairs of flaps (F1, F2, and F3, F4) at both the open ends (18, 22) of the tube piece so that the edges of the flaps (F1, F2, and F3, F4) meet at the centre; and f. sealing a pre-cut cover patch onto the folded and flattened pairs of flaps (F1, F2, and F3, F4) at both the ends of the tube piece to close the open-ends (18, 22) to form the bag. a. overlapping and sealing two longitudinal edges (11a and 11b) of a web to form a continuous tube; b. cutting-off the continuous tube into tube pieces in accordance with desired bag length, wherein each tube piece has at least a first open end and a second open end; c. forming a first pair of flaps (F1, F2) and a second pair of flaps (F3, F4) on the first open end and the second open end, respectively, by folding the ends (18, 22) of the tube vertically, spreading the mouth of the folded open-ends (18, 22) of the tube, and flattening the mouths of the folded open-ends (18, 22) of the tube to form the first pair of flaps (F1, F2) on the first open-end and the second pair of flaps (F3, F4) on the second open-end; d. providing a valve on the second pair of flaps (F3, F4) on the second open end, wherein the step of providing the valve further includes: sealing a cut laminate piece to the second pair of flaps (F3, F4) of the second open end, wherein the cut laminate piece is protruding out of the edge of the second open end of the tube by a predefined offset distance (Do), wherein a mouth distance (Dm) from the longitudinal side of the flattened tube on the second open end is zero so that the valve does not protrude out of the longitudinal side of the flattened tube; and folding the cut laminate piece to form the valve; e. folding and flattening both the pairs of flaps (F1, F2, and F3, F4) at both the open ends (18, 22) of the tube piece so that the edges of the flaps (F1, F2, and F3, F4) meet at the centre; and f. sealing a pre-cut cover patch onto the folded and flattened pairs of flaps (F1, F2, and F3, F4) at both the ends of the tube piece to close the open-ends (18, 22) to form the bag.