Abstract: A layered filtering structure (10) comprises at least a first layer (12) and a second layer (13). Each layer comprises a web of metal fibers which has been sintered. The two layers (12, 13) are in contact with each other. The first layer, most close to the filter inlet side has a porosity below 55%, and the second layer, closer to the filter outlet side has a porosity which is at least 20% greater than the porosity of the first layer. The first layer is compacted in a separate manufacturing step. The layered filtering structure combines the advantage of a small filter rating with a low pressure drop.

Abstract: A pressure resistant sintered non-woven multilayer metal fiber web is particularly useful for high pressure filtration applications (e.g., polymer filtration). The web has a porosity of between 50% and 74%, a weight of between 750 and 1600 g/m.sup.2, and a fiber diameter in each successive layer of between 1.2 to 2 times less than the fiber diameter in the previous layer. The web may be covered with an outer permeable layer at one, or both, of its planar sides.