These sealing discs are used to transport empty bottles and sterile or containing baby milk with a ring and not with the nipple. Moreover, these discs have been designed to fit all types of Advent bottles (old and new model), while the former do not go on natural models. Thus we can carry the bottle quietly in the diaper bag until ready to reheat it to give a baby. I am very satisfied and recommend it to all moms who like to walk with their baby.