Medela Calma Breastmilk Feeding Nipple: 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: - Designed exclusively for breastmilk feeding - Natural feeding behavior encourages easy transition from bottle to breast - Flow control valve allows baby to control milk flow - Milk only flows when baby creates a vacuum - Mimics natural feeding behavior: baby can feed, pause and breathe, similar to breastfeeding - One size/shape nipple for all stages of breastmilk feeding - Comes with 1 Calma nipple Made in the USA