With our new PersonalFit Flex nipple, you can easily adapt the way your Medela breast pump adjusts to help you find the most comfortable and efficient position to express milk, even when your breast shape changes. completely new and personalized pumping experience for you. Personalfit Flex Hopper Size L 27mm. The new PersonalFit Flex breast shield was developed with the help of a team of research scientists and nursing mothers. It is designed to easily adapt to your shape and stimulates your milk flow, helping to prevent milk ducts from squeezing. This makes it easier for each mother to find the pumping position in which she feels most comfortable. The result? A more comfortable and efficient extraction, designed for you. Our research scientists have tested the PersonalFit Flex breast shield in four clinical studies with breastfeeding mothers. Over 1000 pumping sessions have proven it to be more comfortable and effective. Like all Medela products, our Flex pumps are designed to make breastfeeding easier, allowing you to feed your baby your amazing milk for longer.