Enviroflow 20X21X1A (Actual Size) Pollen and Dust Control (4 Pack) Actual Size Measures 20 x 21 x 0.75 MERV 8 Rated. Electrostatic pleated media, which performs better than regular fiberglass fibers. Traps dust and allergens such as pollen, mold, pet dander, and dust mites. Each filter lasts up to 90 days Pack of 4 Filters