Ships in case of 6 only. 96% effective at capturing large airborne particles such as pollen, mold spores and dust mite debris. In addition, the electrostatically charged fibers attract and capture smaller particles that can carry viruses and odors, along with smoke, pet dander, household dust, smog and bacteria. 3M Performance Rating: 2200. 3 Month lifespan. Certified asthma & allergy friendly by the Allergy and Asthma Foundation of America. 20 x 20 x 1