Playtex Drop-In Disposable Bottle Liners are pre-sterilized and leak-proof. Their pre-formed shape allows for one-hand holder assembly, which makes it easy to fill a bottle, even while you're holding your baby. Liners collapse as baby feeds so no air gets into the milk. Help baby transition to bottles with these disposable liners. Playtex Drop-Ins System is similar to the natural sucking, swallowing and breathing patterns of breastfeeding.