Boost protection from the flu and year-round allergies with this all-in-one air purifier filter system. This combination filter has 3 levels of filtration to defend against flu viruses and pollutants in the air; a durable mesh pre-filter, an anti-viral HEPA filter and an activated carbon pellet filter. The filter drum is at the core of purifying your air as it captures 99.97% of airborne allergens and viruses, including the H1N1 virus. To keep your air purifier performing at its best, it's recommended to replace the HEPA filter drum every 12 months (depending on usage). Compatible with all Leitz TruSens Z-3000 / Z-3500 Large air purifiers.