It was fun to read your answers to the post with the picture of the strange pattern piece. Very good those of you who were close or knew the answer!
The welt is also called “origami welt”, I believe Kenneth D. King calls it that. Its main feature is that the seams are not at the sides of the welt, but as you saw in my previous post, on the back. It makes for a welt with less bulk.
Below the steps I took to make the pattern piece for it:
This is the original pattern piece, with foldline and straight of grain indicated.
On the part that will be the back of the welt, two lines are drawn where the seam lines will be. To clarify I’ve marked the seams with line notches.
The seam lines are cut and added to the front part of the welt
The final pattern piece, in paper and in fabric as shown in my “riddle” post. The fabric one is the mirror image, with seams added.
Sew the seams, matching the notches (I added 1cm seams to the pattern piece and made the edge match)
Trim to the points and press.
Turn the welt and press.
Two welts, ready to be inserted in the garment.