Ditch the cheap cord your tent came with.
ULguyline is 1.4mm Dacron polyester braid — 1.7g per metre, 75kg tensile strength, made in the UK. It holds its shape under load, doesn't stretch out overnight, and handles UV without degrading. No re-tensioning at 3am.
 
Available in lengths from 10m to 30m. Tie-out points attach directly to your existing tent loops — a bowline knot works perfectly.
 
Need tensioners to complete the setup? Pick up some UL Line-locs, or grab the complete ULguyline kit with everything pre-cut and ready to go.