Abstract: A balloon comprising first and second balloon sheets and a self-sealing valve positioned between the balloon sheets. Each balloon sheet has a body portion and a stem portion extending outwardly from the body portion and terminating at a stem end. The balloon sheets are bonded together generally around their peripheries to define a balloon body and balloon stem. The stem portion of the first balloon sheet is shorter than the stem portion of the second balloon sheet so that the stem end of the second balloon sheet extends beyond the stem end of the first balloon sheet to define an extended portion of the second balloon sheet. The valve comprises first and second valve sheets each having an inlet end, an outlet end, and an intermediate region between the inlet and outlet ends. The inlet end of the second valve sheet extends outwardly beyond the inlet end of the first valve sheet to define an extended portion of the second valve sheet.