I was lazy and put in the prebuilt coils that came with it. 3.5mm dual coils, don't ask me what kind of wire it is, it is flat.
It is .25 ohm. Flavour is awesome on this thing although it is a bit of a juice guzzler. Mind you, that's probably a lot to do with the coils. Smaller coils, lesser cotton you'll use less juice.
You do have to make sure that your cotton reaches the bottom of the tank though or you won't be able to vape your tank empty.