Abstract: The present invention relates to a pleated filter made of a multi-layer filter medium, including at least one filter paper layer having area weights of 30-100 g/m2, a microfiber nonwoven fabric layer having area weights 5-120 g/m2 and a support nonwoven fabric layer made of synthetic, polymeric fibers having area weights of 10-120 g/m2. The layers of the pleated filter contain fused polymer areas by which the fabric layers are bonded to the paper layer, and by which the fabric layers are made firmer within themselves. When subject to a fractional efficiency test at an initial pressure difference of at most 180 Pa, at a boundary speed of approximately 2.62 m/s and a flow speed through the filter medium of approximately 0.13 m/s, the pleated filter is able to separate at least 90% of particles greater than 0.3 &mgr;m, at least 92% of particles greater than 0.

Abstract: The present invention relates to a pleated filter made of a multi-layer filter medium, including at least one filter paper layer having area weights of 30-100 g/m2, a microfiber nonwoven fabric layer having area weights 5-120 g/m2 and a support nonwoven fabric layer made of synthetic, polymeric fibers having area weights of 10-120 g/m2. The layers of the pleated filter contain fused polymer areas by which the fabric layers are bonded to the paper layer, and by which the fabric layers are made firmer within themselves. When subject to a dust removal test at an initial pressure difference of at most 180 Pa, at a boundary speed of approximately 2.62 m/s and a flow speed through the filter medium of approximately 0.13 m/s, the pleated filter is able to separate at least 90% of particles greater than 0.3 &mgr;m, at least 92% of particles greater than 0.