Honeywell activated carbon pre-filter helps reduce some household odours. Helps capture large particles, protecting the HEPA filter life. To be replaced every 3 months. Can be cut to make 1 to 8 pre-filters depending upon the model. Fits all Honeywell round, QuietCare series models: 50000, 17000, 18150, 40100, 40200 (does not fit hpa tower), and fits air purifiers hpa1000, hpa200 and hpa300.