Hollow fibers are open tube structures with small pores (below 0.1 µm). The pore distribution of hollow fibers can be measured with the POROLUX. Relatively high pressures are needed and a limiting factor is often the burst pressure of the hollow fiber. Therefore, safety is often as concern. Our engineers have developed a stainless steel sample holder in which one or more hollow fibers can easily be glued. The design is such that the pressure can be applied from the outside to the inside or vice versa. With this sample holder very reproducible results can be obtained. The sample holder assembly can easily be cleaned and comes with replaceable O-rings. With this option we have also successfully analyzed hollow tubes.