Patent ID: 8147584

Claim:
A filter composed of a multi-ply filter medium comprising: a) at least one non-woven stiffening layer of synthetic, polymer fibres, a1) the non-woven stiffening layer that is configured to be pleatable, a2) the non-woven stiffening layer having partially oriented and oriented fibres, a3) the titre of the oriented fibres ranging from 2 to 12 dtex, a4) the titre of the partially oriented fibres ranging from 8 to 25 dtex, a5) the non-woven stiffening layer having an air permeability of at least 2500 l/m 2 sec, b) at least one filtration layer which is attached to at least one side of the non-woven stiffening layer, c) at least one covering layer which is attached to the side of the filtration layer remote from the stiffening layer.