Enviroflow 18x24x1 Pollen and Dust Control Pleated Replacement AC/Furnace Air Filter, MERV 8, (exact dimensions 17.75 x 23.75) Pack-4 THE HIGHER THE MERV RATING, THE MORE PARTICLES TRAPPED ? Merv 8 rated AC/Furnace filter. Tested and rated according to ASHRAE Standard 52.2 CREATE CLEANER INDOOR AIR AT YOUR HOME OR WORK - Captures up to 76% of common airborne contaminants such as dust, lint, dust mite debris, pollen, pet dander, smoke, bacteria, and mold spores. BETTER PERFORMANCE ? This Enviroflow air filter is 20 times more efficient than ordinary fiberglass filters EASY INSTALL ? Simply remove your old filter, unpack the new one, insert the filter so the arrow on the side of the frame matches air flow direction, and lastly record the date to keep track of when to change BUY WITH CONFIDENCE ? Every Enviroflow air filter is designed and manufactured in the United States and built to last up to 90 days under normal operating conditions.