hydropneumatic accumulator of the type comprising a sphere having an internal cavity subdivided into two chambers , one chamber containing a gas and the other a liquid . the subdivision is accomplished by an elastic impermeable membrane for the gas and liquid , the membrane being formed and comprising a copolymeric impermeable film including oh groups , and being impermeable to gas , two layers between which the film is incorporated and including an elastic material of a copolymer having blocks of polyamides and blocks of polyethers and a rubber coating of elastic material positioned on at least one of the layers .