Is it normal for bubbles to form in the bottle while my baby is drinking?

SofTouch Peristaltic PLUS™ nipples feature a unique valve with an air ventilation system (AVS™) to enable smooth and comfortable sucking. The bubbles that appear in the bottle form as a result of this system, and are a sign that the ventilation is working correctly. If bubbles do not appear in the bottle, it means that the milk is not flowing properly, and the cap should be slightly loosened for optimal performance.