While deformable particles can push through a monofilament textile, they are held back in three-dimensional needle felts.
Needle felts have a three-dimensional filter structure, whe- reby the filter properties apply both on the surface and th- roughout the depth. This enables deep filtration for very large accumulations of solids and higher fow rates. The needle felt is heattreated on the surface in order to virtually prevent fib- res getting into the filtered material. The specifed pore size is practically unmeasurable; a nominal filter fineness that is based on empirical values is specifed here.