Accumulair FI21.5X23.25A Titanium 1 In. Filter&amp;#44; Pack Of 4 Accumulair Titanium is the highest efficiency Accumulair filter. Electro statically charged fibers capture microscopic allergens smaller than 1 micron&#33;. Unique mini-pleat design helps trap maximum amount of airborne pollutants. Contains odor-reduction technology&#33;. Antimicrobial protection discourages the development of mold&#44; mildew&#44; bacteria or other microorganisms