Specially designed vented valve opens with abby’s sucking actioon. This lets air enter through bottom, helping prevent colic and ingestion of air by baby. The vented valve closes when sucking action ceases insuring a leak resistant bottle when not feeding. Features: Non-Drip design prevents leaks and spills Vari-Flo Valve allows child to control liquid’s flow rate Sure Temp Sensor indicates is liquid is right temperature for child Teething nubs massage and stimulate gums Anti-Colic Air System prevents ingestion of air by baby Requires Wide Neck nipples