I tried rayon, but I get a weird flavor from it. I used it for the first 3 or 4 wicks when I first began my own coils. I didn't like the taste. I tried Koh Gen Do organic cotton & that flavor wasn't there. It wicks great even without peeling the outer layers off, which I never do. I still have some Cellu-Cotton so may have to revisit it just to see, but I have no desire to change.
Kind of agree K and it has its own unique flavor texture. A pro pos, dropped a few lines on the nuances of various wicking media recently on the REOs RxD thread here...READYxWICK for non cotton people | Page 70 | E-Cigarette Forum | #1396. I've done a little research on wicks and winds as some of you know. Def still use rayon. It's worth keeping in the stable for some flavors.
Good luck.