The Playtex Drop-InsTM System is clinically shown to reduce gas, spit-up, and colic and to simulate the natural feeding rhythm of breastfeeding.  The pre-sterilized, disposable liners collapse to keep air out of the bottle and your baby's system. The Premium Nurser Gift Set provides everything you need in one kit. Set includes: 2 - 4 oz Premium Nursers with NaturaLatch Silicone Nipples (Slow Flow) 2 - 8 oz Premium Nursers with NaturaLatch Silicone Nipples (Slow Flow) 15 4