The HEPA filter (High Efficiency Particulate Air Filter) ensures the best possible reduction in pollutants. Ninety-nine point ninety-seven percent of the particles greater than 0.3 micrometers are trapped by the filter. It should be changed once a year. Check the HEPA filter from time to time. Early filter replacement is recommended in the case of obvious discoloration (brown or grey) or visible blockages. It allows for easy filter replacement. Use with air cleaner P2261.