Abstract A process of manufacturing packages form rigid-type foam plastics, preferable foam polystyrene. Such surfaces as are to be joined are heated by direct contact with movable heating jaws until the desired surface configuration having a layer of molten material thereon has been obtained. The surfaces are then immediately put together and subjected to pressure. After the surfaces have been pressed together a shaping member can be urged against them to shape the joint and wipe any excess molten material therefrom. The heating jaw surfaces are preferably oblique relative to the plane of the surfaces to be joined, whereby the surfaces are bevelled and enlarged to produce a high strength, overlapped weld joint. The surfaces to be joined may also be formed with alternating ridges and valleys to further increase the area of the surfaces joined.