My favorite coil so far is just plain kanthal 22ga with 7 wraps on a 2.5mm mandrel. Dual coils usually give me .19 to .20 ohm with this. I use premade clapton wire too and the wrap wire is like 38ga or something. Never paid attention to the core though. 5 wraps of this on 2.5mm gives the same resistance but for the life of me, i cant say the claptons vape any better than the plain kanthal. When i dry burn to clean them off, the plain wire comes off cleaner than the claptons. Crud can get trapped in the claptons i think, even after a hot, glowing dry burn.