Foam Filter for Remstar Pro M Series, Reusable. For use with the Respironics with PR System One, Remstar Plus C-Flex, Remstar Auto A-Flex, BiPap Pro Bi-Flex, BiPap Auto Bi-Flex, Remstar Pro C-Flex, BiPap Pro Bi-Flex, SleepEasy with C-Flex and SleepEasy.