a dry , fabric supported , polymeric gas separation membrane , such as cellulose acetate , is prepared by casting a solution of the polymer onto a shrinkable fabric preferably formed of synthetic polymers such as polyester or polyamide filaments before washing , stretching or calendering . the supported membrane is then subjected to gelling , annealing , and drying by solvent exchange . during the processing steps , both the fabric support and the membrane shrink a preselected , controlled amount which prevents curling , wrinkling or cracking of the membrane in flat form or when spirally wound into a gas separation element .