Have used a tube of stuff called aquaseal in the past to repair waders. They sell it at lots of places like sporting goods stores, walmart, etc. Best if you gunk up a layer and cover with a patch which they sell too but a trick from the oldtimers was to bum a pair old worn out nylons from the wife or girlfriend and cut out a couple of patches and layer on top of each other with enough goop kinda like wetting out fiberglass. Would flex decent and still hold up well on the knees of waders.