Specifically designed for Comotomo Baby Bottles, each pack comes with 2 silicone nipples designed to most closely mimic natural breastfeeding. The naturally shaped, soft silicone nipple is ideal for babies who have trouble transitioning from nursing to bottle-feeding; These replacement nipples have two truly innovative vents that are built-in to prevent colic, while totally eliminating leaking issues; Comotomo Replacement Nipples grow with your baby, and are available separately in 4 stages: truly Slow Flow (1 Hole) for ages birth-3 months, Medium Flow (2 Hole) for ages 3-6 months, Fast Flow (3 Hole) for ages 6+ months, and Variable Flow (Y-Cut) for ages 6+ months (thicker fluids); 2-Pack; Microwave- and dishwasher-safe; BPA-free;.