Clear silicone nipples that fit glass baby bottles. ALWAYS replace the old style brown rubber ones that up until recently came with the Evenflo bottles as they contain cancer-causing agents. The Evenflo bottles we have in stock now come with clear silicone slow flow nipples on them. These 4 packs of extra nipples come in Slow Flow or Medium Flow. I do not carry the fast flow as they are poorly designed with a big "x" opening that chokes babies. I do use the medium flow and they work fine for my toddler. Breastfed babies are used to working harder for their milk, so going with a slower flow nipple works well - they don't get used to the "easy" delivery of bottled milk.