100% cotton, cotton balls, cotton gauze, cotton yarn. I boil mine because when I tried my first build, it had a cottony taste to it, so boiled a big handful for 1/2 hour at a low roll. Some people can't taste it some can, I could. Try it without processing it first, and if you get a cotton taste, boil some out.
Far as amount to use, that's part of the learning process. I unroll the cotton ball into one long strip, then peel off a strip about 3/8" wide, depending on the diameter of my coil, twist it up nice and tight into a strand that will pass through the coil with a slight resistance. Once it's through the coil, I counter twist it to fluff it a bit inside the coil so as not to choke of the
juice supply, then place the tails of the strand where needed for wicking juice. Trim when necessary.
For extern wicking on a vertical mounted coil, my strips of cotton are a bit thinner and I keep it pretty tight so that when I wrap the cotton around the coil the strand will cover the entire surface of the coil when wrapped twice around it without covering the end holes of the coil.
With everything re-buildable one has to play with it a bit to get it right, but once you get it down it is easy to repeat on every attempt.
