Aerostar 21x21x4 MERV 11, Air Filter, 21 x 21 x 4, Box of 4

Nominal: 21 x 21 x 4 Size: 20 7/8"x20 7/8"x3 3/4" 21x21x4, AC Furnace Air Filter High Capacity Comparable to 3M Filtrete MPR 1000 to 1200 Micro Allergen Defense Comparable to Honeywell Allergen Plus FPR 7 Fights lint, dust, dust mites, mold spores, pollen, pet dander, and smoke.