Kanthal wire is both thermally conductive and electrically resistive. When heated, Kanthal wire (iron-chromium-aluminium) builds up an aluminum oxide insulative coating on it's outside surface that protects the individual coils from shorting, one to another. This is called alumina (Al2O3).
This is most clearly noticed when you test fire a well compressed coil... the coil initially shorts and heats unevenly. The more you fire it however, the more evenly it heats - from the center out. This is the alumina layer building up and insulating the coils surface.
For a given length and thickness of wire, the resistance does not change whether it's a 7 wrap conventional coil or a 7 wrap compressed coil. What does change is the amount of heat the compressed coil is capable of generating. Reduced to a short, concentrated segment or element, the heat generated for a given resistance/area can be greater than the sum of parts.
Consider this analogy. Ten matches, lit and separated by 1 inch per match, generate the heat of 1 match or individual heat source, per inch over a ten inch span. Now, light ten matches and place them all within one square inch... follow? ;-)
Last, although "micro" is used to define a small diameter (1.5mm or 1/16" - or less), compressed coil heating element, coil compression need not be limited to that size. In our
vaping application, compression works just as well with 2, 2.5 and even 3mm coils.
