Hevea Standard Neck Bottle Nipples are made entirely of natural rubber, making them safe and non-toxic for both your baby and the environment. The rubber nipple is soft and pleasant for the mouth, but tough enough to chew on without worries! You can wash it by boiling it. Make sure to check it for wear and tear, and replace it with a new one after 6-8 weeks of use. Additional rubber nipples with slow flow and medium flow options are available to be purchased.