Using traditionally-shaped bottles requires tilting the bottle to an uncomfortable upright position and promotes the ingestion of air, which causes colic and gas. The angled shape of the Natural Nurser with vented bottom encourages the proper feeding position for baby and keeps the nipple full of liquid, which helps prevent the ingestion of air and reduces the chance of colic and gas. The specially designed vented valve opens with baby's sucking action. This lets air enter through the bottom, helping prevent colic and ingestion of air by baby. Features: Special vented valve directs air through bottom of bottle Anti-Colic air system prevents ingestion of air by baby Finger pads allow for an easy grip Ergonomic shape encourages a proper feeding position Teething nubs massage and stimulate gums Comes with medium flow nipple - Perfect for milk Requires Standard sized nipples