4.75" x 2.25" washable large-particulate filter. These foam filters are washable with warm water and a mild detergrent. They should be thoroughly rinsed with clean water, and air dry completely, before placing back into your device. Reusable until they lose their intregity and no longer stay positioned within the intake port. These filters are not compatible with the Respironics Legacy, M Series, System One, or Dreamstation models. Please see image for specific BIPAP machine compatibility - Pre-legacy BIPAP Pro with BIFLEX, Duet, Synchrony, etc.