Filtrete Ultra Allergen Reduction Air Filter, 1500 MPR (Previously 1250), 20-inch By 20-inch By 1-inch, Case of 12 Carries a 1500 microparticle performance rating (MPR), previously under rated 1250 MPR. Two packagings may be mixed, with same performance. 90-Percentage effective at capturing particles like dust, pollen and mold spores from the air passing through the filter Attracts and captures microscopic particles that can carry bacteria and viruses 50-Percentage better small particle filtration than our 1000 performance level filter No unnecessary antimicrobial chemicals added. Filtrete filtering material will not support the growth of bacteria, mold, mildew or fungi in normal use.