The Ultra Fine Filters are made by Philips Respironics, made of white fibers and increase the protection of air pollutants when used with a pollen filter in the System One 50 or 50 Series CPAP and BiPAP machines. Higher levels of air pollution (Air Quality Index of 101-150) are one of many reasons a user will add the ultra-fine filter to their machine. Other reasons for users to add the ultra-fine filter are pets in the home, common allergies as well as seasonal allergies. If neither one pertains to you, you can still benefit from the use of an Ultra Fine Filter as it will still add filtration of room air prior to you breathing it through the machine.