Dual Anti-Colic Valves prevent air bubbles from mixing with milk, minimizing your baby's air intake during feeding. The double vents allow air to gently enter the bottle as your baby drinks, preventing a vacuum from forming. By preventing air bubbles from mixing with milk, the dual valves significantly reduce the amount of air your baby swallows. Excess air in the tummy can be a major contributor to colic and gas, leading to discomfort and fussiness for your baby.