Green to Grow colic-relief silicone nipples are made from a transparent, medical grade silicone that is heat-resistant, non-toxic, and odorless. The nipples are free of nitrosamines, a potentially harmful contaminant found in many rubber nipples. Our wide neck option is shaped like a mother’s breast, making it easy for your baby to latch properly and to transition between breast and bottle. Nipples come in three flow speeds; beginner (0-3 months), intermediate (3-6 months), expert (6+ months).