Breastflow is the only feeding system that requires both suction and compression, just like breastfeeding. The nipple is designed to mimic the breast so baby can latch on and to encourage the same mouth and tongue position as breastfeeding. The double-nipple system requires both suction and compression, just like breastfeeding and baby controls the flow of milk. It's the bottle most like breastfeeding. 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. Starter Set includes the following, and is subject to change without notice: two 5oz bottles two 9oz bottles two Breastflow slow flow nipples two Breastflow medium flow nipples one snack container one bottle and nipple brush