With the exception of our glass bottles, all Chicco Well Being baby bottles are made of polypropylene. Polypropylene is resistant, practical and ideal even for older children who start drinking on their own. Reduces the occurrence of colic, burping and irritation. The anti-colic valve prevents the baby from swallowing air, helping to reduce irritation, burping and colic after feeding. The soft and elastic teat makes the change from breastfeeding to bottle feeding and vice versa very easy.