DUO® is an anti-colic bottle that uses a breakthrough medical glass technology that permanently bonds a micro-thin layer of unbreakable INVINCI-GLASS® to the inside of a premium plastic bottle – resulting in the FIRST HYBRID BABY BOTTLE. It features the best of both, the lightweight durability of plastic on the outside and the protective properties of glass on the inside. It won’t stain, discolor, retain odor or funky aftertastes. Most importantly, your precious milk touches 100% pure INVINCI-GLASS. It's dishwasher, bottle warmer, and electric sterilizer safe and has minimal parts, making it easy to clean. Award-winning Duo features the exclusive INTUI-LATCH® nipple with a 9 out of 10 acceptance rate by infants, breast-like flow, natural feel, and anti-colic valve. Available in single packs, two-packs, and gift sets. *5oz. and 9oz. bottles come with Stage 1 Slow Flow Nipples (0m+). Gift Sets also include (2) Stage 2 Medium Flow Nipples (3m+). Stage 3 Fast Flow Nipples are sold separately.