There have been several threads along this line. Searching brings up this thread, for example, in which Steve provides burn test guidelines. There was also a thread and link (which I can't find just now, sorry) to a fellow's website where he addressed the question exhaustively in the context of having a very special kilt made with all sorts of hidden meanings in thread count, pleat count, not stitched on the Sabbath, etc. That site might give you some additional insights, I'll keep looking or perhaps another member has it to hand.