The cold or hot fomentation bag forming structure includes a bag body having a bottom, an upper opening, a folded end formed on an upper edge and a folded portion adjacent to the folded end, wherein the folded portion has a predetermined length a bag opening member disposed on the upper opening and connected to a cover opening or closing the bag opening member a neck portion extending from the bag opening member and at least one elastic gasket holding the neck portion and held by the folded portion and at least one collar holding an outer surface of the elastic gasket and an outer surface of the folded portion.
