a flat , flexible , sterilizable container for a liquid to be maintained and extracted under sterile conditions , said container comprising : a body having walls formed by a three - layer laminate including an outermost layer of a propylene polymer , an innermost layer of a copolymer of ethylene with a small amount of butylene , and an intermediate layer of an amide polymer ; and a valve carried by said body comprising an elastomeric core whose spaced major faces are covered , one , by a three - layer laminate similar to said body wall forming laminate and , the other , by a two - layer laminate including a first layer of a copolymer of ethylene with little butylene and a second layer of an amide polymer .