Ace Liquid Silicone Rubber Nipples are free nitrosamines. Ace teat are made from 100% Liquid Silicone Rubber the same material used for making artificial heart valves. They are simply the best possible rubber you can buy for your baby. Ace silicone teats are completely clear and they stay that way forever, unlike latex teats. Regulated anti-colic device - lets air into the bottle as baby sucks. This stops the nipple from collapsing, enabling the baby to get a steady stream (flow) without gulping air. Ace teat will not build up sticky residues. Ordinary latex teats always do