NUK First Choice Plus Glass Baby Bottles are easy to fill and clean, due to their extra-wide neck opening. The glass bottles are made using High-quality durable glass, that is chemical free and safe for your baby. The teats used have been specially modeled on a mothers' nipple during breastfeeding, making these bottles feel natural in your baby's mouth. While leaving enough room for your baby's tongue and jaw to perform natural sucking movements which help in the natural oral development.