These nipples are made from a medical grade silicone that is heat-resistant, non-toxic and odorless.  Free of nitrosamines found in other nipples.  Shaped like a mother's breast, these nipples make it easy for baby to latch on to a bottle and transition between breast and bottle easily.

Green to Grow Wide Neck Beginner Nipple        0-3 months
Green to Grow Wide Neck Intermediate Nipple        3-6 months
Green to Grow Wide Neck Expert Nipple        6 months+