Most customers in their feedback online had negative comments about these nipple shields staying attached to their skin during the breastfeeding and not being the right size for their nipples. As you can see from the product listing on this page, these shields come in several sizes according to the size of the mother’s nipple. The most common sizes offered are 20mm and 24mm, which are small and medium. Some women said the ones they purchased were either too large or too small, making them not work properly. The manufacturers are very good about returns and refunds for these, so it should not be a big problem. As far as the adhering to the skin, the silicone material needs to be moistened first before it will stick to the skin. The material is thin to allow this to work well.