Re: Double foil
I have experimented with double foil, and I cannot tell the difference. Physics: A .005mm piece of foil, will transfer 99.9999% of the heat right through it. The basic purpose of the foil, is to hold the coals away from the tobacco, and create an "air cushion" to moderate the heat of the coals.
My best success, has been to keep just enough hot coal on the foil, to produce a moderate smoke, and to rotate the coals frequently (12oclock, 3 oclock, and so on). If you put too many coals on top, and create a "bonfire", you will burn up the flavor, and the tobacco will scorch,etc.
Try two foils, and one foil, and see. If your smoking session is more enjoyable with two foils, then fine.