Our patented Duo-Flo nipples have valves that flex and adjust the flow of milk according to your baby’s feeding pace, so your baby can drink without interruption or nipple collapse. This minimizes the air going into your baby’s stomach which can reduce colic, gas and spit-up. All Avima Duo-Flo nipples are made from 100% High Quality Silicone. It is durable, taste free and odor free. Dishwasher and Sterilizer Safe. The silicone is soft and smooth for your baby’s comfort and to help transition from Mom's breast to bottle feeding. Avima Duo Flo Nipples are available in 3 different flow rates: Stage 1 / Slow Flow – Marked with a 1 on the base. Recommended Age 0-3M. Stage 2 / Medium Flow – Marked with a 2 on the base. Recommended Age 3-9M. Stage 3 / Fast Flow – Marked with a 3 on the base. Recommended Age 6M+. All age indications are approximate, as babies develop at different rates. Flow rates are according to ASTM global standards. When your baby tries to drink the milk very quickly or shows frustration during feeding, it may be time to move on to a faster flow rate.