Better for baby - better for mother.Bottle LinersEnergizer PcIMPORTANT NOTE: If you are using these new expandable Drop-Ins liners in your current Nurser, use the liner for ounce/mL measurements, not the holder. Our new holders have updated ounce markings to match the new liners 1. Open package at bottom, remove liner. 2. Place liner into Nurser and fill. 3. Pull nipple through retainer ring and screw onto Nurser. 4. Discard after single use.