Our single hull stainless steel bottles also offer more convenience! Plastic and glass have innate insulating qualities. Stainless steel does not, therefore stainless steel heats and cools more quickly. It also allows you to gauge the temperature of the contents through the bottle much better than glass or plastic.. Lid doubles as a measuring cup or snack cup. Nipples use a peristaltic "stretch & contract" design that helps to reduce the risk of colic, spit up and ear infections. "Life bottle" system transitions baby from bottle feeding, to Sippy cup, to a lunchbox friendly water bottle by simply using the appropriate accessory.