Do it Best MERV 10 efficiency rated electrostatic HVAC (Heating Ventilation and Air Conditioning) air filters are 40 times more effective than standard fiberglass filters. Protects against microscopic allergens, smoke odors, grass pollen, oil, smoke, tree pollen, ragweed pollen, mold spores, dust mite debris, pet dander, and lint. Low airflow resistance saves on energy costs while still protecting furnace and air conditioning units. Lasts up to 90 days.