I'm more-or-less with Allaerra on that one. For me, it's either Corbin or polypropylene. I like both, and I think the choice should be based on your saber design, the LED color, what kind of "feel" you're going for, etc. But I think mixing them defeats the point of both styles. It's a choice between evenness (polypropylene) or that cool blurred (?) core effect (Corbin). I love the way polypropylene looks when the saber is turned off. It looks almost like a shaft of mercury.