A method of making a spiral wound membrane cartridge, which method comprises the steps of: providing a central permeate collection tube and a plurality of sheets of feed spacer material, permeate carrier material, and semipermeable membrane filtration material, said membrane filtration material sheets each having a length about twice as long as said other sheets and being folded approximately in half, adhesively attaching each of said permeate spacer sheets between half-sheets of two different semipermeable membrane filtration sheets with bands of adhesive which extend along both longitudinal side edges of said permeate carrier sheet and across the free outer end edge thereof to create a plurality of 3-ply leaves, disposing a feed spacer sheet between each two facing half-sheets of the same sheet of filtration membrane material, spirally wrapping said plurality of 3-ply leaves and feed spacer sheets about said central permeate collection tube, and associating a thin tubular shell having textured exterior surface with said tensioned assemblage to provide a filtration cartridge which allows a controlled bypass flow of liquid feed between a pressure vessel interior surface and said textured exterior surface of said shell, characterized in that said assemblage is overwrapped with sheet material to create a substantially cylindrical element and with a tension to retain said assemblage of sheets in radial compression, wherein the overwrap sheet material has a tensile strength in the longitudinal direction of at least 1,250 N/m (7.0 lbf/in) and wherein: a) the element has an outside diameter of 100 mm (4 inches) and the tension in the overwrap sheet material is at least 300 N/m (1.7 lbf/in) or b) the element has an outside diameter of 150 mm (6 inches) and the tension in the overwrap sheet material is at least 660 N/m (3.7 lbf/m) or c) the element has an outside diameter of 200 mm (8 inches) and the tension in the overwrap sheet material is at least 890 N/m (5 lbf/in) wherein the radial compression is achieved by affixing said overwrap sheet material to an end portion of one of said feed spacer sheets, wrapping said overwrap sheeting about said assemblage for at least about four complete wraps while applying a gradually increasing tension until said tension is reached to provide the element having the desired tightness, then slightly unwrapping while maintaining said tension to provide the element with a precise selected outer diameter, and then joining said overwrap sheeting to itself and severing said overwrap sheeting material adjacent said joint. providing a central permeate collection tube and a plurality of sheets of feed spacer material, permeate carrier material, and semipermeable membrane filtration material, said membrane filtration material sheets each having a length about twice as long as said other sheets and being folded approximately in half, adhesively attaching each of said permeate spacer sheets between half-sheets of two different semipermeable membrane filtration sheets with bands of adhesive which extend along both longitudinal side edges of said permeate carrier sheet and across the free outer end edge thereof to create a plurality of 3-ply leaves, disposing a feed spacer sheet between each two facing half-sheets of the same sheet of filtration membrane material, spirally wrapping said plurality of 3-ply leaves and feed spacer sheets about said central permeate collection tube, and associating a thin tubular shell having textured exterior surface with said tensioned assemblage to provide a filtration cartridge which allows a controlled bypass flow of liquid feed between a pressure vessel interior surface and said textured exterior surface of said shell, characterized in that said assemblage is overwrapped with sheet material to create a substantially cylindrical element and with a tension to retain said assemblage of sheets in radial compression, wherein the overwrap sheet material has a tensile strength in the longitudinal direction of at least 1,250 N/m (7.0 lbf/in) and wherein: a) the element has an outside diameter of 100 mm (4 inches) and the tension in the overwrap sheet material is at least 300 N/m (1.7 lbf/in) or b) the element has an outside diameter of 150 mm (6 inches) and the tension in the overwrap sheet material is at least 660 N/m (3.7 lbf/m) or c) the element has an outside diameter of 200 mm (8 inches) and the tension in the overwrap sheet material is at least 890 N/m (5 lbf/in) wherein a) the element has an outside diameter of 100 mm (4 inches) and the tension in the overwrap sheet material is at least 300 N/m (1.7 lbf/in) or b) the element has an outside diameter of 150 mm (6 inches) and the tension in the overwrap sheet material is at least 660 N/m (3.7 lbf/m) or c) the element has an outside diameter of 200 mm (8 inches) and the tension in the overwrap sheet material is at least 890 N/m (5 lbf/in) wherein the radial compression is achieved by affixing said overwrap sheet material to an end portion of one of said feed spacer sheets, wrapping said overwrap sheeting about said assemblage for at least about four complete wraps while applying a gradually increasing tension until said tension is reached to provide the element having the desired tightness, then slightly unwrapping while maintaining said tension to provide the element with a precise selected outer diameter, and then joining said overwrap sheeting to itself and severing said overwrap sheeting material adjacent said joint.