COMFORTABLE: The unique fitting system of the Elvie Stride Pump Breast Shields ensures greater comfort, correct nipple alignment and effective suction. | BABY SAFE MATERIALS: Elvie Stride 21mm Breast Shields (2 pack) are made with the highest quality BPA free plastic (polypropylene) to ensure durability and safety. | SIZE GUIDE: The 21mm Breast Shield is made to fit nipple widths that measure between 16mm and 18mm. The size of your nipple can change over the course of your feeding journey, which may require a different size Breast Shield to be purchased for the best fit. | EASY TO CLEAN: All washable components should be cleaned after every use, either using warm water and mild dishwashing soap or in the dishwasher, and sanitized once per day. Sanitize parts in boiling water for five minutes. Also suitable for microwave, steam or cold water sanitization.