PersonalFit Flex Membranes are extra membranes for your PersonalFit Flex Connectors, which are included with Medela's Freestyle Flex, Swing Maxi, Pump In Style with MaxFlow and Solo Breast Pumps. As part of your regular pumping routine, be sure to examine your pump parts. If you notice damage or extensive wear, replace the part immediately. Medela recommends replacing your membranes every 3 – 6 months, depending on your pumping frequency. IMPORTANT: Use of pump parts or accessories not designed for your specific breast pump may cause irreversible damage to the product. For that reason, only use the accessories that came with, or are identified by Medela to work with, your specific breast pump model. Each pack contains two (2) silicone membranes.