The Playtex Drop-Ins 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 Decorated Bottles Gift Set includes: 3 - 4 oz Premium Decorated Nursers with Slow Flow NaturaLatch Silicone Nipples, 2 - 8 oz Premium Decorated Nursers with Slow Flow NaturaLatch Silicone Nipples, 30 Drop-Ins Liners, 6 Nipples in a variety of flow rates, and Instruction Booklet.