Colic in infants can be caused by a combination of influences including ingesting air during feeding. The Advanced Comfort range from Closer to Nature is specially designed to reduce air ingestion that may cause colic. The discomfort which can be caused by ingesting air when bottle feeding can be stressful and upsetting for both parents and babies. This bottle set comes complete with four 260 ml/9 fl oz feeding bottles and four slow-flow teats. The teats do not feature a valve, unlike other Closer to Nature teats, and so they must not be used with standard bottles without a venting tube.