I have been wanting to try a method like what Barb describes with the scraps of MacGillivray she sent with my kilt. Though to give tartan stability and to keep it square as I would work with it (largely to match stripes), I wanted to block it square and press a layer of one-sided fusible interfacing across the entire inside surface of the tartan before I cut it down to intermediate size. Next, I'll fold the sides over the back, press flat, and then apply another strip of interfacing nearly the width of the finished flash down the back. This is the way the the flashes I purchased were constructed as far as I can tell.

I'm having difficulty finding thin, black, single-sided fusible web, though. I may look at upholstery shops next.

I made denim flashes from an old pair of jeans a few weeks ago using a thicker, two-sided fusible interfacing, being sure to press the raw edges as close to each other as possible to minimize length-wise fraying. Because the webbing was so thick, I left the top inch or so of the flash fuse-less to make it easier to stich down the loops in the second-to-last step and I did not apply a second layer of webbing on the outside.

Regards,
Rex.