This in-line air filter is designed to cleanse and purify the air as it leaves the CPAP, BiPAP, or Bilevel machine and travels into the tubing. An extra step in CPAP filtering, the in-line filter ensures that the airflow traveling to your mouth is extremely clean and free of pollen, dust, or tobacco smoke particles. Compatible with most CPAP, BiPAP, and BiLevel machines, the filter connects to standard 22 mm CPAP tubing and installs easily on your machine. Please note: This filter may affect an auto CPAP's ability to judge the correct pressure necessary during the night. If you use an auto-adjusting CPAP, please contact us before purchasing this additional filter.