What determines friction, string or coating? The string is covered up by a coating, so I don't see how the string could influence friction. If you reach the point where the coating has been frayed, the bare string will have poor playability and snap imminently. So, I don't think it is the string that influences friction. Which makes you wonder, why don't gut or nylon use the same coating as slippery polys or zyex? Or perhaps it is a surface lubricant that separates poly's from gut and nylon. I don't remember anything in TWU's COF testing method that would fully remove a lubricant. I will look into that later when I get the time.