Flanges are the horn shaped part that actually touch the breast. You also need to be mindful of the flange you’re pumping on. Most companies will send a standard 24mm flange. Sometimes they’ll send a larger size as well. They can’t send every flange size they make as that would be expensive and create too much waste. But they don’t always make it clear that the flanges that come with the pump are not one size fits all. And in my practice I hardly EVER use the 24 or bigger flanges unless we’re using a silicone insert. For almost all of my families we’re sizing down. Some times significantly smaller. 

The fit of the flange can make or break your pumping experience. Too small and friction can cause pain and even damage (and pain makes it difficult for milk to let down). Too large and the breast may not be stimulated well, which inhibits your let down to have milk flow. When too much areola is pulled into the flange, the tissue swells around the nipple pores and can prevent milk from efficiently emptying from the breast, resulting in plugged ducts, pain, tissue breakdown, and eventually a reduced milk supply. Using too large of a flange from the beginning may even prevent you from bringing in a full milk supply. Do you ever pump for 20+ minutes and still feel like there’s milk in there? Most likely too large of a flange. The stimulation from the pump is triggering you to make more milk, but the size of the flange is preventing you from emptying that milk efficiently. Poor flange fit can also impact the suction of your pump and how well it functions with your body. If you have the suction all the way to the highest level and aren’t emptying well, you flange is too big.