The polyester-free AirSense 11 Disposable Hypoallergenic Filter is designed to improve air quality and protect your AirSense 11 CPAP or APAP machine from large airborne particles such as dust, pollen, as well as finer particles. The hypoallergenic filter is not washable and should be replaced every 2-6 months. If the filter becomes discolored or dirty sooner, it should be replaced to ensure optimal filtration.