The Honeywell HRF201B pre-filter can be used in a variety of Honeywell Air Purifiers. A built-in carbon pre-filter layer has been added and can be instrumental in capturing 99% of airborne particles at 2 microns from the air that passes through the filter. It also reduces household odors such as pet, cooking and smoke odors. For the very best performance, it is recommended that the HRF201B HEPAClean Replacement Filter U be replaced every 4 months. This selection of Certified Honeywell Filters are compatible with the following units: HHT270 and HHT290 (Tower models require 2 filters). Included is 1 Dual Action Filter and the Master pack is a 4 piece display tray.