Specially designed for use with Playtex nurser bottles. Convenient disposable liner collapses to keep air out of the milk. BPA free. What makes the Playtex nurser with drop-ins liners different? Drop-Ins Liner: As baby feeds you can see the soft liner gently collapsing to prevent air from mixing with the milk and getting into baby s tummy. This means less gas and less discomfort for baby. This is a 150 count box. Each clear liner holds 4 fl oz.