a breathing bag including a connector portion and a distensible portion manufactured by a process including the steps of providing moldable material , forming a portion of the moldable material into the connector portion of the breathing bag and forming another portion of the moldable material into the distensible portion of the breathing bag . the moldable material may be provided by extruding a parison of thermoplastic material ; the connector portion of the breathing bag may be formed by compression molding and the distensible portion of the breathing bag may be formed by blow molding or blow and vacuum molding ; such distensible and connector portions are formed or molded integrally . a one - piece breathing bag including integrally formed neck portion and distensible portion with the neck portion having a wall thickness sufficiently thick to permit the neck portion to be connected directly to a male fitting and with the distensible portion having a wall thickness sufficiently thin to permit the breathing bag to expand and contract in delivering breathing gas to a patient .