Sorry, this is so belated my comp. went on frits.
Poly leaders are made by coating a mono core with clear, flexible polyethylene. You'll notice that they are slightly bigger in diameter then plain mono leaders. They're supppossed to have a lower specific gravity. Ones that are pure polyethylene float. According to Tom Rosenbauer poly leaders can realy punch a fly with short tippet section and can straighten a tippet section of 8 feet long for spooky fish. I'm thinking about trying this for fishing streamers and lrg. nymphs. Then a floating poly for possibly my small stream rig. Advantage of poly over braided is that they can't hold H2O so there's no spray and you don't have to dress the leader. I think the first people to make these was Airflo out of UK which is available in U.S. & I'm not sure if LRO carries these or not. Hope this helps.