Compatible with the X-3400A and X-3700 Air Scrubber, this 2 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. Replace as needed when indicator light illuminates and other filters have been checked for blockages.