Multi-ply filter medium

The present invention relates to a filter composed of a multi-ply filter medium which (i) has at least one textile stiffening layer (layer 4), preferably a non-woven layer, of synthetic, polymer fibers, glass fibers or mixtures of the same, (ii) at least one filtration layer (layer 3), which is attached to at least one side of the non-woven stiffening fabric, the filtration layer being made up of glass fibers, (iii) at least one further filtration layer (layer 2), which is applied on the filtration layer according to ii), the further filtration layer being made up of glass fibers, and at least one textile cover layer (layer 1), which is applied on the filtration layer according to (iii), the cover layer being made up of synthetic polymer fibers. A further subject matter are filter modules including a housing and at least one filter medium according to the invention, and also a method for producing the filter medium according to the invention and also the filter modules and the use thereof in filtration of air/gas and liquids, preferably for filtration of air flows in supply air and/or heat exchanger systems.