Every woman is unique - one breast shield size does not fit all. That is why Medela offer a wide range of personal fit breast shields sizes to allows mothers to choose the breast shield that is the right size for them, to ensure maximum comfort and efficiency when pumping. All personal fit shield ensures the best chance of ensuring milk volume and good breast emptying, Individual and personalised fit helps to prevent nipple trauma, convenient for travelling or for when you do not have time to clean your breast shields and need extras. BPA free - safe for you and your baby.