The Spectra Backflow Protector Replacement is designed for Spectra S1, S2, S3, and 9 Plus Breast Pump models. It is a pivotal component of the Spectra closed system. The Spectra Backflow Protector ensures your breast milk is free of outside contaminates and prevents Breast Milk from making its way into the Breast Pump motor. The Spectra Backflow Protector is specifically designed to maintain performance and efficiency of all Spectra Breast Pump Models. If you are double pumping, you’ll require two Spectra Backflow Protectors. One (1) Spectra Backflow Protector for one breast. Includes (1) silicone membrane, (1) uppercase, and (1) lowercase Weight : .050kg.