Kanthal A1 is a ferritic iron-chromium-aluminium alloy (FeCrAl alloy) rated for use at temperatures up to 1400C (2550F).
The alloy has high resistivity and great oxidation resistance.
At present Kanthal A1 is the best coil material for ecigs.
The factors that affect resistance are:
Diameter: The thinner the wire (higher gauge number), the higher the resistance per foot. The thicker the wire (lower gauge number), the lower the resistance.
Length: The longer the wire, the higher the overall resistance. The shorter the wire, the lower the overall resistance.
Temperature: The more heat the wire generates, the more resistance it will create.
Current: Determine the current (amperage) you need to heat your kanthal wire.