Green to Grow regular neck baby bottles are made from PES plastic, which gives them a natural golden color. They are free of phthalates and free of bisphenol A – a suspected hormone-disrupting chemical used in polycarbonate plastic, from which most baby bottles are made. Nipples for their bottles are of a medical grade silicone that like the PES in the bottle is also considered heat-resistant and non-toxic. The nipples are free of nitrosamines, a potentially harmful contaminant found in many rubber nipples.