The pleated cartridges are made of galvanised steel, stainless steel or synthetic materials, depending on the type of gas to be dusted. They provide both the benefits of a large filter surface and can be cleaned and reused several times. The cartridges are suspended side by side in a filtration box opened at its base by a funnel through which the dust is recovered and evacuated. The dust loaded gases pass through the cartridges from the outside to the inside. The use of these cartridges is recommended for the retention of very fine dust and/or the filtration of gases loaded with acid or aggressive pollutants.