The certified HEPA media filter catches and holds ultra-fine dust preventing it from escaping the vacuum. It is 99.97% efficient when used with the RIDGID DV0500 Ash Vacuum. This filter is intended to pick-up fine dust and ash that would be produced by a pellet stove, fireplace, grill or smoker. Cleans the air by filtering 99.97% of particles as small as 0.3 microns Specially designed HEPA filter to filter fine dust and ash Ideal for wood/pellet stoves, BBQ grills and fireplaces Filter only to be used with the RIDGID DV0500 ash vacuum