Abstract: This invention relates to a method of forming a bag. The method includes the step of forming a line of weakness in a portion of material being used to form a part of the bag, placing a patch over the line of weakness, and forming the bag. The arrangement and construction is preferably such that the patch is located substantially inside the bag thus formed. The line of weakness and patch may preferably act as a self-closing opening for the bag. A bag which includes such a self-closing opening, and bag machinery used for forming such a bag, are also described.