Playtex Pre-Sterilized Disposable Liners are soft yet strong collapsible baby bottle liners for use with the Playtex Nurser System. All liners are pre-formed and leak free for convenience to drop them in Playtex nursing bottles. The liners have pre-calibrated markings for measuring ounces. Playtex Pre-Sterilized Liners are ideal for storing breast milk, providing baby with a clean, fresh bottle for each feeding.