Bacteria in food multiplies quicker when stored at room temperature, the Nanobebe Transition Milk Bottle allows breast milk to be spread into a thin layer that cools quickly, reaching ideal refrigerated temperatures 2 times faster than standard bottles. It also warms 2 times faster than standard bottles, satisfying baby’s immediate hunger needs. The bottle’s domed shape and concave base make it ideal for tiny hands. It has an advanced, 360° venting system with two vents that release air even when covered by baby’s mouth, which reduces colic. These feeding bottles are also stackable, so you can save storage space and track pumping order. As opposed to Nanobebe’s 5oz breastmilk bottle, the stage 2 transition bottle can hold up to 8oz (about 237ml) . BPA, PVC, Lead and Phthalate free.