A screw closure (2) is provided on a soft packaging (1), preferably a film bag. Said screw closure consists of a first part, which consists of a spout having a fastening flange (4) for connecting to the soft packaging (1), and a second part (2) in the form of a screw cap (5). The screw cap has a top surface (50) and a lateral wall (51) having an internal thread (52) present in the lower region. Above the internal thread there is a thread-free portion (53), in the upper region of which a sliding seal (10) is arranged. The sliding seal (10) presses on a likewise thread-free region (7) of the spout above the external thread (6) disposed on the spout. A screw closure that is leak-proof even during unscrewing is thus achieved.