This Nilfisk Microfilter is like a white fabric bag, fitting over the bottom of the motor. It retains 99.5% of all particles to 2 ?m, cleaning the air quite well before it reaches the motor and final ULPA or HEPA filter. It should be replaced after you use ten paper bags to keep your Nilfisk performing well. This filter is for use in Nilfisk's Allergy and commercial vacuums in the GM, GS & GD series, not in their Family Vacs. This filter was formerly known by part #616821. For similar products see our list of Nilfisk Vacuum Supplies.