Aerostar 20x25x4 MERV 8 filters are comparable to MPR 600 and FPR 5. Designed for superior filtration efficiency, these filters are made with electrostatically charged synthetic material that draws and captures allergens between 0.3 - 1.0 microns. Aerostar filters are a simple and cost effective step towards a healthier home environment. They also improve the efficiency of your HVAC unit and therefore reduce maintenance and utility costs, by removing dirt and reducing strain on the motor. For best results, change the filter every 60 to 90 days but increase frequency to 30 days during peak summer and winter months when your unit is working the hardest. Compatible with furnaces and AC units.