| 摘要 |
A filter medium ( 11 ) comprises at least a first ( 12 ) and a second layer ( 13 ). Both first and second layer have a layer volume VLq and a layer filtering surface SLq, where SLq is the accumulation of all mantle surfaces of the fibers present in this layer q. The first layer has a SL 1 /VL 1 -ratio of less than 32500 m<SUP>2</SUP>/m<SUP>3</SUP>, and the second layer has a SL 2 /VL 2 -ratio being more than 1.1xSL 1 /VL 1.
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