This combination filter drum has three levels of filtration. Designed to defend against flu viruses and pollutants in the air, it features 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 the air as it captures 99.97% of airborne allergens and viruses, including the H1N1 virus. Compatible with all Leitz TruSens Z-2000 / Z-2500 Medium air purifiers.