protective bags made of a plastic film have heretofore been produced by folding two pieces of films by hand , and it is very difficult to mass - produce asymmetrical bags at a low cost . protective bags made of a film bearing any design are now continuously produced at high speeds by using a film tube blank , inserting a floating separator in the film tube blank , forming openings with symmetrical or asymmetrical continuous or discrete cut lines in the upper and lower surfaces or in both side surfaces in a state where motion of the film tube blank is stopped , depending upon the length of the bag , and cutting the film tube blank at the melt - adhered portion using a cutting edge extending in the direction of width .