Our signature stainless steel Narrow Neck bottles feature a thin, tall body shape which is easy for baby to hold. our Narrow Neck bottles include: Accordion Flex peristaltic silicone vented nipple with a stretch and flex action that creates the ideal bottle feeding conditions and reduces the chance of of gas or colic. Seal tight, leak-proof and color coordinated bottle ring that eliminates drippy messes during feeding Stainless steel lid to keep the nipple clean and doubles as a 2oz measuring cup for perfect breast milk measuring and preparing formula