What material to use for non metalic pull-pull setup?
Instead of spyderwire I use powerpro fishing line. Also used the K&S kevlar thread, and the kevlar pullpull mentioned in an earlier message. No stretch, stronger than anything.
Just don't hit the power-pro with a heat gun because it melts. . Kevlar will not melt.
I tie the line directly thru the hole in the servo horn. Use a fisherman's knot, and slide the knot to snug the line. then lock the knot with some thin CA. On the control surface end, I tie the line to a 2-56 eyebolt screwed into the clevis. This provides some adjustment for later.
I have used this on rudders, elevators, split elevators, and water rudders (floatplane) with never a problem. The only time I ever got slack was using a 4-40 stud for a rudder horn, and the rod bent and relieved some tension. Never broke a string yet, and I've been using this for 6+ years.