Texture in sprang

One of the students' projects in my class used thick and thin warps alternating, two thin loops and one thick loop repeatedly. It was coming out so nicely that when I got home I wanted to try it myself.  I used the warp I had on my frame already, and added some thin cotton seine cord between the thick cotton twine/cord I'd been demosntrating with in class.  Here's how the structure looks when stretched.  You can see clearly what the thick pair of warps does in the fabric.  I love the cabled look between the lacy bits:

But look at all the folds that happened when I took it off tension and sewed it up into a little bag!  I think this is so cool, all the movement that it has.  It's doing this on its own.  I have not tried to block it out.  This seems kind of like the "tracking" patterning that sometimes happens spontaneously in plain weave fabric.