I rebuild wick and coil assemblies for a friend who owns a shop and I am proud to say, customers come in and request the rebuilds I have done rather than new ones. They are telling my friend, they find the rebuilds work better and last longer. In the course of doing this I have used wool, fiberglass, and silica wick materials and 32ga and 34ga kanthal wire. I would like to increase the turns in 1.8 ohm coil, so iam going to change to 28ga Kanthal or 30 ga nichrome 60. K A1 32ga is 0.7 ohms/inch, 28ga is 0.4 ohms/in., and NiC 60 is 0.6 ohms/in. It doesn't sound like much, but it will allow another two coils in a 1.8 ohm coil which will provide more vapor.
As for wicking, I use mostly silica and prefer 2mm for 6 strand long wick asseblies and a 2mm and a 3mm in 4 strand assemblies. If forced into a single wick situation I'll use 3mm or, rarely, cotton. Cotton wicks like a thirsty camel after a month long desert crossing, but is more difficult to work with. Bottom wick assemblies are easy to rebuild. I use 1 pc of 2mm and 1 pc of 3mm wrapped together inside the coil, but you have to be careful NOT to wind the coils to tight.
Surprising enough, factory made wick assemblies are not as close to the labeled value as you would think. There tolerance is +/- 0.3 ohms. Think about it, a 1.8ohm coil can be between 1.5 and 2.1 ohms. In the long run, this means very little to the user. Only a real techn - geek, like me, would know or care.