Very probably the most "mysterious" and contentious part/component/material in the Original Quad ESL.  It is, within the constraints of this design, the very best optimization possible.  Don't believe me?  Read: The Review. You can also take a look at the Nylon .vs. Graphite debate below.  However, as Ben Openshaw says in his review, "The nylon coating that Gary has come up with is the single best conductive coating for the Original Quad speakers that I have used to date; it beats soap, graphite, and everything else I have tried. It seems to work well only in the Quad type designs. If you need to match a more conductive coating it does not work that well. So it will not work in all situations. "  Modesty compels me to add, that I was just following the indications from the patent and that I later found soluble nylon that would dissolve in alcohol, which was a great relief from using Phenol!