The Small Blue Mitsubishi Anti-allergy Enzyme Mini Split Filter is a two-pack of replacement anti-allergy air filters for Mitsubishi Mr. Slim s heat pump and air conditioning split systems attached to the unit s plastic framed pre-filter. The filter captures airborne bacteria, viruses, and germs and traps fine dust and pollen that the larger post-filter may not catch. This filter is made with a special enzyme to break down the bonds in allergen proteins, giving your home or office fresh air while reducing the presence of allergens in the environment.