Introducing Calma: Designed exclusively for breast milk feeding. Switching from bottle back to breast has never been easier. Calma was developed using evidence-based research on babies' natural feeding behavior so you can enjoy your breastfeeding bond longer. With Calma, the milk will only flow if your baby works and creates vacuum to remove the milk. This enables the feeding behavior learned at the breast to be used with Calma. Features & Benefits Vented nipple: Helps avoid gassiness as the bottle is vented through our unique air-control system; Mimics natural feeding behavior: Supports easy transition from bottle to breast. Research has shown that with Calma, your baby is able to maintain the learned feeding behavior that your baby exhibits when breastfeeding; Flow control valve: Allows baby to control milk flow. Milk only flows when baby creates a vacuum; Calma doesn't drip: You can turn Calma upside down and it still won't drip. Your baby needs to apply a certain level of vacuum in order to get milk out; One size/shape nipple: For all stages of breast milk feeding. The flow, shape and length of Calma are designed to suit your baby's needs as your baby grows; Compatible with all Medela breast milk bottles; Breastfeeding must be well established before introducing Calma; Made without BPA: All parts that come into contact with breast milk are not made with BPA; What's Included: 1 Calma nipple with lid;.