Miele SF-AH 50 Active HEPA filter for Models S4, S5, S6, & S8, Garden, Lawn, Maintenance Uses activated charcoal filter to absorb odors Traps 99.99% of all particles as tiny as 0.3 microns Needs to be replaced after 50 hours of use, or approximately 12 months Designed for Miele S4 and S5 series canister vacuum cleaners