Furnace filter. 12-in x 24-in x 1-in. Made of fibreglass. Captures airborne microparticles including smoke, smog and airborne allergens such as pollen, pet dander and mold spores besides large particles like dust and lint. Lasts 3 months. Meets the "American Lung Association Health House Indoor Air Quality Guidelines" (1,000 Microparticle Performance Rating - MERV 11). No unnecessary antimicrobial chemicals added. "Filtrete" filtering material will not support the growth of bacteria, mold, mildew or fungi in normal use.