Abstract: A thin film membrane formed to a predetermined shape is produced by bending the membrane to create a loop and softening the membrane that makes up the loop with either thermal energy or a swelling solvent. The softened loop is then drawn between plates or about a mandrel to form a membrane with a predetermined fold radius. The fold region produced by the method of the instant invention does not require an adhesive sealant to prevent unfiltered liquid from diffusing through the membrane. The method is especially well suited for preparing membranes for use in the production of spiral wound filters.