method and apparatus which facilitate the tearing of packing materials and the like into desired lengths by pre - tearing them along the rows of perforations which are provided for that purpose . in the disclosed embodiments , a packing material having inflated chambers separated by rows of perforations is fed at a predetermined speed in a direction generally perpendicular to the rows and periodically pulled upon rather abruptly to produce a partial tearing of the material along the rows of perforations .