Feature Sits tight in the neck of your Haakaa breast pump and will stop any spills or accidents. Made from 100% silicone. Fits in both 4 oz (100 ml) and 5 oz (150 ml) size breast pump. Clean after each use. This product can be sterilized with any steam sterilizing system or boiling water. No bleach based agents. Small parts. Not for babies to chew on. Keep way from babies and young kids.