The patented Natural Flow internal vent system eliminates the vacuum and the air bubbles found in most baby bottles. It allows air to enter through the teat collar, without being incorporated into the formula. This means that babies are able to feed more comfortably because the vent allows babies to feed without fighting the negative effects of a vacuum or the discomfort of ingesting air bubbles. This reduces colic, burping & wind. 9 out of 10 Healthcare Professionals recommend this product for colic relief.