Direct-flow filtration combines a filtration cycle operating in dead-end mode with regular intermittent backwashes. Such filtration module is achieved by efficiently capping one end of the crossflow device so that all the fluid is forced to pass through the membrane walls. This paper focuses on the operational considerations and design aspects of the direct-flow filtration membrane modules, specifically pressure driven inside feed (PDI) format. PDI is commonly used since it permits effective backwash and long term stability. The axial dependence of the transmembrane pressure (TMP) and the cumulative filtration volume is studied under non-fouling conditions. Geometrical parameters including fibre radius, fibre wall thickness, fibre length, module void fraction and imposed average flux are varied over a broad range values encompassing the values applied in today's water industry. Two performance parameters are introduced: the module productivity parameter, and the filtration uniformity factor. Suggested design ranges for fibre diameter, fibre length and packing density are given. Taguchi's method is applied to determine how much each parameter contributes to the overall filtration performance.