Replace lost or damaged parts for Dr. Brown's custom flow double Electric and Dr. Brown's Single electric Breast pumps with these closed-system membranes. The 100% silicone membrane acts as a barrier between breast milk and the pump tubing and works together with other pump parts to create strong suction. Replacing membranes will help maintain that suction over time. Package comes with (2) Two replacement membranes. Replace every 3-6 months. Dishwasher (top rack) and sterilizer safe. It is recommended to use a small parts dishwasher bag. Bpa free.