XPOWER Stage 4 HEPA Filter for AP-1800D Air Purifier SystemStage 4 HEPA Filter for AP 1800D Air Purifier System Compatible with the XPOWER AP 1800D Portable HEPA Air Filtration System, this 11. 5 inch thick, professional HEPA filter captures contaminants such as bacteria, allergens, mold and even 0. 3 sized sub micron particles at a rate of 99. 97%. Several pre filter air scrubber stages ensure a long life of this filter. Efficiency rating up to 99. 97% against 0. 3 micron particles Compatible with XPOWER AP