A filter medium (100) having an inflow side (110) and an outflow side (120) defining a flow direction (190). The filter medium comprises at least n consecutive layers Lx of fiber media, x varying from 1 to n, n being more than or equal to 2. Ll (101) is the layer of the n consecutive layers closest to the inflow side of the filter medium and Ln (103) is the layer of the n consecutive layers closest to the -outflow side of the filter medium. For all layers Lx of the at least n consecutive layers, the ratio Hx/ (kx*Ax) is substantially identical, 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. The fiber media of at least part of the layers of the filter medium comprises metal fibers.