Hi guys...I'm using a three part epoxy mold which I inflate with a bladder. The flanges are pretty smooth based off polypropylene board and a quick polish but I still get a build up of thin resin film on the flanges that  is a witch to remove. My release process is zyvax sealer and Zyvax release 4 with a dusting of hairspray as a lazy substitute for pva. (The spray gives my parts a slight texture which is desirable).
Clean up is to throw the mold in a water bath for a day. I wonder if the long soak if effecting the zyvax but my parts pop out from a complex mold super easily.
Maybe a build up on the mold flanges is just normal...it polishes off ok but that's all extra work.