Proper venting is critical in preventing vacuum effects and reduces air intake by your baby;The unique design has 4 lock notches that fit perfectly into the bottle's neck, eliminating over and under tightening which can cause leaks and/or inconsistent liquid flow;The vent ring is made from hard PPSU plastic that is co-molded with a soft silicone vent sleeve;This unique, one-piece design allows assembly while only touching the hard vent ring, keeping the silicone vent sleeve that comes into contact with the feeding liquids away from unsterilized hands