Clean series absolute ratting filters The clean series melt-blown absolute filter cartridges are designed with extruded different density layers of polypropylene fibers. The unique PLC control technology sufficiently turning up the filtration efficiency level 99.98% for particle sizes encoded in the identification markings. The cartridges have two layers of fibres wound on a polypropylene core. The outer layer is equal to pre-filter and the inner layer qualified as a final filter to be the best from appearance to applications.