A filter module with a perforated inner tube (20) and a concentric, perforated outer tube (22), forming an interposed annular gap for a filter membrane (10) pleated into folds. The membrane folds (11, . . . ) are of different fold types with differing fold heights, extend from a respective fold edge (111, . . . ) resting against the outer tube towards the inner tube to the respective fold tip (114, . . . ) and are arranged along the circumference of the annular gap as groups of folds (11, . . . ) of different types. Each group has a mating fold (15) which extends from a mating fold edge (151) resting against the inner tube towards the outer tube to the mating fold tip (154). The height of the mating fold is no more than the difference between the width of the annular gap and the height of the fold type with the shortest height of the same group.