Spectra Baby USA’s innovative design ensures that all Spectra Baby USA breast pumps have backflow protection for hygienic, safe pumping. This backflow protector creates a complete physical barrier between your milk and the pump motor, ensuring that your milk is protected and that pump performance is maintained. This backflow protector is suitable for use with the following breast pumps: Spectra S1, Spectra S2, Spectra 9 Plus, Spectra M1. If you are double pumping, please buy two. Discounts for higher quantities.