he Classic Nipples are made from soft silicone and feature.These special vents are designed to prevent nipple collapse, and promote a more comfortable feeding experience for baby.Unique valve on the nipple flexes to your baby's feeding rhythm. Milk will only flow at the pace chosen by your baby to minimize overeating and spit-up, burping and gas. This nipple is made from silicone - a BPA-free material and as your baby feeds, the unique valve on the nipple flexes to allow air into the bottle instead of your baby’s tummy.This nipple gives you a best result and keeps your baby smooth soft and happy.