The vent's tabs fit perfectly into the bottle's neck, ensuring a proper fit and eliminating leaks or inconsistent liquid flow;The bottle does not require assembly and there is no need to touch any part that comes in contact with the milk or formula;Made from durable polypropylene plastic, each bottle is individually shrink-wrapped to deliver the highest level of cleanliness;The 9-ounce bottle includes a Stage 2 nipple (medium; 3+ Months);Silicone nipples are molded (not cut) with the appropriate size hole and tested for consistency