Martma nipples are designed to resemble a mother's nipple during breastfeeding. These Extra Slow Flow nipples deliver breast milk or baby formula at a slow and steady pace, satisfying the appetite of newborns. Anti Colic Nipples-Dual Air vent invented help prevent colic during feeding. Help with easy transition from breastfeeding to bottle feeding. All products are made from BPA-free materials for maximum safety. These nipples fit all bottles and are suitable for both breast milk and formula. Due to their unique flat and symmetrical design. This baby bottle nipples fit perfectly into baby's mouth. They also fit all Martma feeding bottles.