Free passages in a filter element. These pores are only of equal size on metal meshes and . On the majority of tissues used, on the other hand, they are very different, as they are formed by the irregular arrangement of fibres that are often of varying thickness (Figure F 17).
For this reason with tissue filters it is only possible to achieve a particle distribution, as given in the contamination classes.
Figure F 17: Pore formation in plastic tissue