Abstract: The apparatus comprises means (31, 33) for guiding and for holding the longitudinal edges of the film to be sealed so that they overlap with an intimate and distributed contact and comprises in an opposing position, a short distance from these guide means, a sealing head (6) made in good thermal insulator and with a low coefficient of friction in relation to the film, which directs onto the said film jets of hot air at an appropriate temperature and an appropriate pressure, through longitudinal slits of appropriate dimensions (35). The sealing head is connected to supply and control means (39-44) that keep it fully operational or have it promptly fully operational, the head being mounted on means (45) for moving it rapidly towards or away from the film to be sealed.