Abstract: A zip plastic bags comprising at least one strip of a flexible material (2) for packaging which is stuck to the opening region of the bag, two strips of semi-rigid material (1a, 1b) attached along said flexible strip (2) which have at least one tongue (3) and groove (4) so that the tongue (3) of one semi-rigid strip (1a, 1b) can be inserted into the groove (4) of the other semi-rigid strip (1a, 1b), thereby latching the strips(1a, 1b) one to another, a clasp (5) that grasps these strips (1a, 1b; 2) in joining of separating manner as it slides along the strips (1a, 1b 2) and a tab (6) attached to the clasp (5) for sliding the clasp (5) and for tearing open the bag, when opened the first time, with the aid of sharp protrusion or pin (7) positioned on the tip of the tab (6).