Abstract: The specification discloses apparatus for forming individual heat sealed articles, e.g., tubes or bags, from a strip of two superimposed layers of heat sealable material or of a material coated, or impregnated, with a heat sealable material which apparatus comprises means to feed the strip in a zig-zag configuration and means for welding together the layers of the strip at or adjacent the transverse crests of the strip located on one side of the zig-zag. The welding means comprise a single continuous welding device and the feed means includes means for supporting the strip at the transverse crests located on the mentioned one side of the zig-zag and for presenting those crests to the welding device.