Our lansinoh glass baby feeding bottle and natural wave teat has been designed with avs (air ventilation system) that reduces potential causes of colic. The lansinoh natural wave teat has been clinically proven to encourage baby's natural feeding pattern, helping maintain established breastfeeding patterns, making it easy to switch from breast to bottle and back again. Glass is the most inert material used for baby feeding bottles. there is no molecular transfer of any kind between the contents and the feeding bottle itself. The lansinoh glass feeding bottle is made from a special type of material called borosilicate glass. borosilicate glass is less dense, more resistant to thermal shock and often used in laboratories and better for the environment