3M™ Capillary Membrane MF-PP Series. Capillary and tubular membrane MF-PP Series. Inner diameters range from 50 µm to 5500 µm. These capillary membranes are widely used in the food and beverage industry, in waste water filtration and sterile filtration. MF-PP Series capillary membranes are also ideal for use in heavy-duty filtration