It actually wicks
Rayon fibers transports liquid, while cotton absorbs it. Long story short, when I began rebuilding I used silica, then Ekowool, then cotton and Japanese cotton. And I always had wicking problems in tanks. Either dry hits or flooding. Take the Fogger RTA I have. I hated building on it, since it just was a PITA, and then it would either burn or leak. Then I tried rayon. And it began to work. During the process of learning how to use rayon, I had one leak early on, but that was it. The next rebuild, it went through 50ml of eliquid without a single problem, never a dry hit and never a leak. The only reason I re-wicked was curiosity.
I also think the flavor is better than cotton or silica. For me, it just works. JeremyR showed me the way and I couldn't be happier. Because of him, I love the Fogger now, and every other RTA and dripper I use. I can go a month without having to re-wick, and when you have a dozen rba/rtas that lets me enjoy life, and my other hobbies, again.