Patent ID: 8449642

Claim:
A filter medium having an inflow side and an outflow side defining a flow direction, said filter medium comprising: at least n consecutive layers Lx of fiber media, x varying from 1 to n, n being more than or equal to 2, L 1 being the layer of the n consecutive layers closest to the inflow side of said filter medium and Ln being the layer of the n consecutive layers closest to the outflow side of said filter medium, wherein for all layers Lx of the at least n consecutive layers, the ratio Hx/(kx*Ax) is identical within measurement tolerances, wherein Hx is the average thickness of the layer Lx in flow direction, Ax is the average surface area of cross sections according to planes perpendicular to the flow direction, and kx is the permeability coefficient of this layer Lx, wherein Hx varies for each of the Lx layers, and wherein the fiber media of at least part of the layers of the filter medium comprises metal fibers.