Shaun the sheep video notwithstanding, if one were tied to a chair and forced to put up with that over and over, how long do you suppose it would take before you'd go stark ass bleating crazy?

Once upon a long time ago, it was postulated as to how natural wool yarn was less abrasive to glider canopies. I have not data one way or the other, but one could order natural wool or synthetic yarn for their MK#. Most chose natural wool.

I've tested yarns and found synthetic yarn lasts longer. I've also done testing of the MK# yaw strings, holding a curved acrylic surface out the window of my truck, to mimic a glider canopy, so I could view the string from the side. Due to the design of the MK# base, the yarn streams back maintaining the lift and separation imparted by the base, and looks to maintain that separation all the way back not appreciably touching the canopy at all.

With a normally maintained canopy, no scratching. If left parked out, uncovered, and with blowing dust or sand, I'd expect any string or yarn material might cause fine scratches. Loose covers can cause deep scratching.