DESC: Aniti-colic valve flexes to allow air into bottle to prevent vacum build-up; air bubbles move away from nipple and into bottle, not into baby's tummy Naturally shaped nipple promotes proper latch-on, easy to combine breast and bottle feeding Wide bottle shape for easy filling and cleaning, dome cap seals nipple for spill-proof mixing and transportation East to combine breast and bottle feeding BPA -Free Bottles are made from Polyether Suphone (PES) - a BPA-Free material with a natural honey-colored tint