Comotomo Nipple-Packs are replacements specifically designed for Comotomo Baby Bottles. Each pack comes with 2 silicone nipples designed to most closely mimic natural breastfeeding. Our naturally shaped, soft, silicone nipples are ideal for babies who have trouble transitioning from nursing to bottle-feeding. Each replacement nipples also have two truly innovative vents that are built in to prevent colic, while totally eliminating leaking issues. Available in 4 stages: Truly Slow Flow (1 Hole) 0-3 months Medium Flow (2 Hole) 3-6 months Fast Flow (3 Hole) 6+ months Variable Flow (Y-Cut) 6+ months (thicker fluids)"