The Spectra Duckbill Valve Is Designed To Increase Suction And Provide Better Output During Breast Pumping Sessions While Preventing Backflow Contamination. Each Duckbill Valve Is One-Piece, Making It Easier To Clean And Lasts Longer. Spectra Duckbill Valves Are Made Of Silicone And Quality Tested To Ensure A Sturdy Grip On Small, Medium, Large, Or X-Large Breast Shields And Flanges. All Spectra Breast Pump Parts That Come In Contact With Breast Milk Are Bpa-Free. For Use With Spectra S1, S2, Sg, And 9 Plus Breast Pumps.