Being that sil-nylon stretches, I'm guessing it would be best to reinforce cuben with cuben.
However, with vain rearing its ugly head, I'm hesitant to use cuben as the only extra cuben I have to make reinforcing with is yellow...and the cuben I'm wanting to reinforce is a light green. And, those two colors together, I'm shamefully going to say, would be...well, ugly. A guy has to have some pride! Any way, I do have some black sil-nylon that would at least be the same color as the zipper, stitching and tie-outs.
The reinforced area I'm talking about would only about 1" square...right at the top of a zipper.
What do the MYOGers here on BPL think?