The Spectra Air Cap replaces the tubing outlet cap on your Spectra S1 Plus.
This part is necessary when a user wants to single pump. These are made of silicone material.
Above all Spectra Baby strongly recommends using only original accessories along with Spectra Breast Pumps. In order to avoid any issues with your breast pump, which might void your warranty.
Note that the Spectra Air Cap does not require washing/ sterilising.