Broan-NuTone VX3918STD Bag Standard Filter Media Bags for VX550 and VX1000 Series, 8-Gallon, 3-Pack Standard filtration provides reliable performance through the use of a two-ply electrostatically charged media filter, resulting in a cleaner home and improved indoor air quality Filter media captures particles down to .10 micron at 85% efficiency, ensuring a clean and healthy environment Suggested replacement about twice a year for maximum performance and efficiency