Abstract: A multilayer filter pack includes at least three adjacent layers of fibrous material, each of which is permanently electrically charged and not more than 10 mm thick. The upstream and middle layers are formed from fibers having a fiber diameter that decreases from layer to layer in the direction of flow and are arranged at a packing density that increases from layer to layer in the direction of flow. The third layer has a fiber diameter and packing density that is approximately equal to the fiber diameter and packing density of the first layer. The multilayer filter pack is particularly well suited for use in air-purifying systems and breath protection filters.

Abstract: A process of producing a pliable roller uses a flexible strip of material with a tension element longitudinally therealong, the tension element having a lesser longitudinal extensibility than the flexible strip of material. The tension element and the flexible strip of material are fixed together and portions of the flexible strip of material are longitudinally folded together along the tension element. At least after the fixing, the flexible strip of material with the tension element longitudinally therealong is wound, longitudinally, about a roller core in such manner as to form contiguous windings thereabout projecting outwardly from the roller core.