Never used. $10 total Philips Avent Anti-colic with AirFree vent bottles are designed to reduce feeding issues: such as colic, gas, and reflux. The unique AirFree vent is designed to draw air away from the nipple keeping it full of milk to avoid air ingestion. This vent also keeps the nipple full of milk even when the bottle is held horizontal, allowing for upright feeding. Feeding in an upright position can help to reduce reflux and aid in digestion. The nipple shape is designed for a secure latch for a comfortable feed. The bottle is easy to clean and assemble with few parts. The AirFree vent is only one piece and is easy to clean without any special tools. The Anti-colic bottle features a valve, integrated into the nipple, that reduces vacuum buildup and reducing air into your baby’s tummy. The Anti-colic bottle can be used with or without the AirFree vent, giving you the option based on your baby’s feeding needs. The soft silicone nipple is available in different flow rates for babies of all ages, flows 1-4. We recommend using the Philips Avent Anti-colic baby bottle with Philips Avent Anti-colic bottle nipples. Includes 2 4oz Anti-colic bottles with AirFree vent with Flow 1 nipples.