the opposite and vertical jambs 2 and 3 are linked together at the top by a roller drum 4 for a flexible curtain 5 the jambs 2 and 3 have an integral guidance device 6 for the flexible curtain 5 for its movements between a closed position and an open position it will be observed that the flexible curtain has sleeves 5 a in which the horizontal reinforcing cross pieces 5 b are inserted their ends engaging in the guidance devices 6 fitted on each jamb 2 and 3 fig2 each guidance device 6 has two straps 6 a and 6 b fitted one opposite the other to provide on each jamb 2 and 3 a guideway 6 c for the curtain 5 and its cross pieces 5 b for the sake of clarity and understanding only the guidance device 6 on jamb 2 will be described since the other fitted on jamb 3 is identical the straps 6 a and 6 b of the guidance device 6 each have at one end a loop 6 d 6 e each of which fits onto an end point formed by a holding pin 6 f 6 g built into the jamb 2 holding pins 6 f and 6 g are arranged one opposite the other and close to the drum 4 holding the curtain 5 of the door 1 at the bottom of jamb 2 there are two tensioners 6 h and 6 i forming the other ends of the guidance device which respectively hold the opposite.