The Minimum Efficiency Reporting Value (MERV) is used by manufacturers to explain how efficient the air filter is at trapping airborne particles. A higher MERV rating means cleaner air but reduced air flow. MERV 8 filters capture 80% of airborne particles like pollen, dust mites, mold spores, and pet dander down to 3 microns in size. MERV 11 air filters capture up to 95% of the above mentioned airborne particles down to 1 micron in size. If you choose a MERV 13 filter expect greatly diminished airflow but improved filtration of bacteria, tobacco smoke, and cooking oil down to 0.3 micron in size. Before you choose a MERV rating check with your HVAC manufacturer to see what your system is designed to handle. Picking the wrong filter can impact air flow and reduce equipment life.