Enviroflow 21x23X1A (Actual Size) Pollen and Dust Control (4 Pack) Actual Size Measures 21 x 23 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