The Thinkbaby system follows your baby through each stage of feeding, from bottles to sippies to straw cups. Our Stage A and Stage B nipples were made in order to reduce the number of nipple variations that parents need to purchase. This not only saves money, but also reduces the challenge of identifying which flow rate works best. We recommend Stage A nipples for 0 to 6 months. The vented design reduces vacuum pressure while your baby nurses, and encourages healthy feeding habits. The extra-soft, medical grade silicone tip mimics natural breastfeeding with its cross-cut design, reducing spillage.