Nickel is a ferromagnetic, commercially pure (99.6%) wrought Nickel with good mechanical properties over a wide range of temperatures, high ductility, and excellent resistance to many corrosives (in particular hydroxides).
It has roughly the strength of mild steel when annealed and can provide higher strength levels when in the "as rolled" condition.
They are twisted, so as to reduce the resistance of the coil but still maintain a high coverage on the wick.
One factor that affect resistance is the diameter of the coil,the thinner the wire (higher gauge number), the higher the resistance per foot. The thicker the wire (lower gauge number), the lower the resistance.
With these prebuilt coil, it will make DIY easier, there are 5 resistances for your choice.
Only use the Nickel coils when using a temperature limiting mod, like Hcigar HB DNA 40W Box Mod or Smok M80 Plus
Do NOT use Nickel coils on ANY mod other than those with temperature limiting.