 that's sealing the duct work from the inside out so that we don't have to like take sheetrock down and try to seal up a bunch of joints and whatnot and by doing that um kind of like a garden hose right you have water if you got a couple leaks in it uh where is it going to go pass the least resistance so it's going to start to leave all the leaks and by the time you get to the end to sprinkle on your garden