What is the significance of the tinned straneded copper wire?

Is it more conductive?  If so, why not just use a larger stranded copper?


chris

I am putting warmfloor in my daylight basement in Montana.  80023 is the project number for Ductmasters.   

Will there be any problem with putting a plastic sheeting vapor barrier, 1/2" of extruded polystyrene with 1/4 of particle board under the elements? 

We will be carpeting over it, and the warmfloor is supplemental heat for the basement. 

The other thought i had was doing thin set mortar over the top of the elements, but i am afraid this will make the floor feel hard.

The diagrams show putting the insulating and element layers together, but i read in another post that putting the elements on a plywood layer is ok.

If i left anything out please let me know,

chris