SDA Type desodorising cartridge that also provides very effective particle retention : the SDA type cartridge offers several levels of air treatment... the central filtration media consists of 1 layer of active carbon paper + 1 layer of polypropylene canvas rolled up. a pre-filter then an anti recycling separation at the end are provided by two separate sleeves in polyester felt that is wound around the central filtration media. perforated internal and external cages provide rigidity and hold the unit together and are glued at both ends with polyurethane into two stainless steel shells. the SDA type 10/05 cartridge is made using moulded end pieces.