Abstract: Two superimposed layers of thermally weldable material are welded to one another at welding zones delimiting respective receptacle preforms having respective open ends and connected in series to a transporting strip which extends longitudinally of the processing path of displacement of the receptacle preforms. The goods to be packaged are introduced into the respective receptacle after the two layers of the respective receptacle preform have been separated by blowing a stream of air into the receptacle through the open end thereof. Thereafter, the open end of the receptacle preform is closed and the receptacle preform is severed from the transporting strip to obtain a filled receptacle which is freely transportable. The welding operation is performed by a welding roller which has an electrically resistive conductor wire mounted thereon along such a course that, when developed into the plane of the superimposed layers, the conductor wire will coincide with the zones to be welded.