Mmmm, no, the canvas interfacing isn't there to keep sweat away from the wool. I can think of many a hot day of piping when my kilt has been soaked right through to the kilt belt. The canvas interfacing in a trad kilt is there to stiffen the kilt and help it keep its shape. The way the interfacing is fan-folded parallel to the pleats gives the kilt rigidity up and down the body (to keep the kilt from buckling) but allows the kilt to flex easily around the body.

I haven't any idea why PV kilt don't have interfacing. Cost issues, maybe?? Adding interfacing would add to the construction time. But, if I were making one, I'd probably include it for the same reason that a trad kilt has it - stabilization and rigidity (although it wouldn't make any sense unless the pleats were stitched down). What to use? Sew-in Pellon doesn't have the flex of woven hair canvas, but it should work and would be washable. I'd do the same kind of fan-folding with Pellon that I would do with woven interfacing. You could also probably buy a heavy cotton canvas, pre-wash it to shrink it, and use that.

Barb