I'd venture, if you're to use them, that nylon is superior to polypropylene in all the areas ChicagoNewport27 cites, especially abrasion and UV resistance. My experience with them tends to support somewhat artbyjody's impressions though. Whichever type you pick, I'd get extra because it's not at all unlikely that they'll jam up to the point where you'd be most inclined to cut them off rather than fight with them any further. Other than that, a great idea.
“Scientists are people who build the Brooklyn Bridge and then buy it.”
Wm. F. Buckley, Jr.