The Zoo Friends Anatomic Nipple is soft flexible, winged silicone nipple that adapts to baby"s mouth helping to keep air out of baby"s tummy. The winged shape helps fit the corners of baby"s mouth which reduces air intake and helps keep milk in for less gas and fussiness. Micro air vents help to prevent or reduce nipple collapse by balancing air in the bottle. The silicone nipples are easy to view liquid in the tip of the nipple. The 4 pack Nipples include a special brush designed to clean nipples. The nipples are for use with Zoo Friends bottles, but also fit Evenflo Classic bottles.