Can your breast milk storage bags pass the drop test? Dr. Brown’s 6 oz/180 ml Breast Milk Storage Bags feature an extra-durable design that cushions in case of drops. The Breast Milk Storage Bag’s extra-durable design works overtime, with additional exterior trim to cushion in case of dropping. Double zip seals keep the air out while the super-thick material keeps the breast milk fresh in the freezer or fridge.