16x25x1, Filtrete Ultra Allergen Reduction Furance Filter Air Filter, MERV 11, by 3m 3M Filtrete 2001DC Ultra Allergen Filters are sold in cases of six. This filter is 90% effective at attracting and capturing large airborne allergens like pollen&#44; mold The Filtrete Ultra Allergen Reduction Filter carries a 3M Microparticle Performance Rating (MPR) of 1250 Contains electrostatically charged media to filter and attract particles in the air. Attracts and captures microscopic allergens like: Smoke&#44; Pet dander&#44; Household dust&#44; Smog&#44;