Optimal Mamilla Extra Wide Neck – Double Anti – Colic System (300ml) 0+ is made of high grade polypropylene. It provides a real smooth inner neck and a seamless interior. Dirt or unmelted milk would not be able to accumulate inside, thus, it is easy for the mother to thoroughly clean. Inspect nipple before and after use. Throw away when worn, damaged or punctured. Before each use, wash thoroughly. Do not leave nipple in sunlight when not in use. The bottle can be sterilized at high temperature, sterilize the teat and feeding bottle 8 minutes with optimal sterilizer. Boiling is not recommended. Steam sterilizer is safe.