Breastflow is the only feeding system that requires both suction and compression, just like breast feeding. The nipple is designed to mimic the breast so baby can latch on and to encourage the same mouth and tongue position as breast feeding. The double nipple system requires both suction and compression, just like breast feeding and baby controls the flow of milk. It's the bottle most like breastfeeding. The Stage 2, Medium Flow Nipple is perfect for infants and formula feeding, and fits all Breastflow bottles. The Breastflow System is ideal for nursing moms who would like to introduce a bottle, are returning to work, or need to supplement while their baby is in day care or with a caregiver. Because Breastflow bottles so closely mimic the feel and action of breastfeeding, care givers can bottle feed baby while Mom is working and Mom can still continue to breastfeed.