I put in three pieces (underapron, pleats, and apron) of hair canvas. This is not your typical interfacing. It is very a stiff, woven fabric made from goat hair and synthetic fibers. Basting is done in white thread and will come out later. It’s hard to see against the light-colored canvas. Permanent tailor stitches are done in black “carpet” thread. Yes, they are messy, but they will be covered up by the lining later on. None of the permanent stitches show on the outside. The kilt is wider at the hips than at the waist, so the canvas over the pleats has folds in it that accommodate the change in width.