These bottles have been created with a silicone teat which babies instinctively like, thanks to the patented Silk surface. With the Silk Teat the switch between Breast & Bottle feeding is made easy. BPA free & made with a vented base to ensure a unique natural flow principle to ensure a smooth milk flow. These features reduce colic & keep baby calm & relaxed. The best feature is that these bottles are self sterilising saving parents a huge amount of time.