The Respironics Reusable Filters are an extremely important to protect your lungs and airways by air filtration and trapping large particles. Filters are an extremely important part of your therapy. Reusable filters protect your lungs and airways by air filtration and trapping large particles that inhabit our air, such as fibers, cat and dog hair and dander. With your purchase you will receive a reusable filter, and it is recommended that you hand wash and air dry it frequently. (Especially if you smoke or have pets.) Replace your filters every three months to maintain your machine and successful sleep therapy.