Product Description Calma is an innovative feeding solution designed exclusively for breastfed babies. With Calma, the milk will only flow when your baby creates vacuum to remove the milk. There?s a reason, Calma looks different than other nipples on the market. The unique shape is research based and is designed to allow baby to be in control of the feed due to Calma?s built-in valve system that releases milk only when baby creates a vacuum. Yes, there is only ONE Calma size! Calma is designed to adjust to your baby?s suction strength as your baby grows, so you do not need to purchase different nipples for different stages. The length, shape and flow of the nipple was determined by clinical research and is suitable for the full-term babies. The opening of Calma is not indicative of the size of the milk flow. The milk actually flows through a very small hole inside the Calma. The flow speed is dictated by your baby: slow flow for the small baby to faster flow as your baby grows and gains sucking power. Calma helps avoid gassiness as it is vented through our unique air-control system. Plus, Calma doesn?t? drip so you don?t have to worry about cleaning up spills, allowing you to spend more time on what matters! Calma is made without BPA, DEHP and other phthalates. What?s Included: (1) Calma nipple; (1) Cap; (1) Lid Manufacturer Contact Information customers can contact Medela Customer Service at 800-435-8316 ,they can also use the form at the following link: http://www.medelabreastfeedingus.com/contact-us