NilfiskCFM oversize 18 pleat main star filter with shiny PVC coating for 560mm diameter containers. These are used in the CFM3707 and the CFM3907 for use with lots of fine dust.
The PVC membrane makes it easier for dust to fall away from the filter into the dust container. HOWEVER, heat may cause it to go tacky and require replacing.
At the moment, as postage is capped at a maximum of $20, maximise the saving on postage and buy some of the related parts below, such as dustbags and a new hose, or a new floor tool and some other accessory!