NIPPLE INFORMATION The nipple is equipped with a valve that lets out air when the baby closes down on the nipple thereby flattening the nipple to shape naturally after the baby's oral cavity. SHIELD INFORMATION The round lightweight shield faces away from the sensitive and delicate skin around the baby's mouth to ensure minimum contact with the baby's nose and mouth, which means less chance of moisture build-up from saliva that can cause rashes and sore spots. The shield comes in one size no matter the nipple size. The shield is made of 100% safe food-grade PP.