Getting a good fit when pumping is essential.  A flange that is too small can cause nipple damage, a flange that is too large may be painful and both can decrease the amount of milk that you are able to pump. If you have the right size flange, your nipple will be centered in the tunnel of the flange and not rubbing on the side. There should be a small space all the way around the nipple during the entire pumping session.  Sometimes breast tissue will swell so even if it starts out looking fine if your nipple eventually starts rubbing on the inside of the tunnel, consider trying a larger size. This video shows what a proper fitting flange should look like throughout the entire pumping session. Feel free to watch the video and contact us if you have questions.