I've been doing some research on what type of cord to use for resligning some hexes, and I found something very surprising here.

Basically, the paper seems to suggest that while the tensile strength of high performance cord vastly outperforms nylon, the strength once it's tied in any sort of knot is significantly less. It also suggests that while other materials might outperform nylon when new, several of them rapidly degrade when stressed, to a tensile strength well below ordinary nylon.

Is this just a fluke? Is regular old 5mm nylon really the best choice with a rating, for example, of just 5.6 kN for slings? (Given the average breaking strength of a loop of 7mm nylon tied with a double fisherman's was rated at about 5/3 of the tensile strength, I'd think it's probably a -3-sigma rating pretty close to 9kN when tied... Obviously not tested though.)

It seems odd that it isn't more well-known that nylon is the best choice if it's true... Everyone seems to swear by high performance rope for slinging chocks and setting anchors, but it seems the "high performance" rope might just offer a better sounding number than an actual performance increase.

Has anyone had any experiences with cord failing on a piece of pro? What failed, when? What's worked? What do you trust? Does anyone have any other info on the failure of rope when in actual climbing configurations, and not just the tensile strength?