Tip of the nipple has smaller diameter and gets bigger as it reaches the base. This makes it easier for a brand new calf to get it positioned in its mouth. The vent design has a very large base and slit that works together with the accordian style ribs that open and shut with movement as well as suction to increase airflow. 6ct pkg or each.
This helps the larger more aggressive calves get the air they need to drink faster. It also helps absorb side pressure so the nipples don't pull off. You can actually carry the bottles by the nipple. Goes on the bottle with a gentle push. It also has a softer material and texture that feels more natural.