Single coils- Resistance=Resistance...easier to work with..especially in carto-tanks.
Dual coils- More surface area...a lot more stress on your battery..Unless you can direct the liquid to the coil, they suck (dual coil carto in tank)
1/equivalent resistance=1/resistance+1/resistance...for instance, a 1.5 Ohm dual coil is:
1/equivalent resistance=1/3 + 1/3=2/3
resistance=1.5
A properly functioning dual coil will contain two resistors, double the resistance of measured resistance. So you can have an increased amount of power from the lower resistance of the over all circuit, but since you have two 3 ohm coils, you can increase the voltage dramatically when compared to the same 1.5 Ohm single coil.
I just got into micro coils..they're really fun. A micro coil has its coils touching each other, instead of having gaps in between them. Fantastic vapor production..wow.
I'm trying to figure out the real difference between mico and nano coils.