There is disclosed a method and an apparatus for making a medium-filled packing of two superposed heat-sealable elongated webs of plastic film (3) which are thermally sealed in longitudinal and transverse directions of the film webs for forming packings (11), and where the formed packings are filled by medium and closed. The film webs (3) are passed between a pair of rollers (6) which are pressed against each other, retaining the film webs therebetween. Thermal sealing across part of the width of the film webs is performed so that unbroken longitudinal areas (9) without any thermal sealing appear in the longitudinal direction of the film webs (3). The medium is filled into the packing before closing it for the formation of the medium-filled packing.