Opinions on 6mm Kevlar Cord

The local gym has Sterling Powercord on a spool. I think that a single strand is rated to something huge like 17 kN. Does anybody use this stuff? What are your opinions on it?

Worth the extra cost over nylon? Is it only good for tying hexes, or do you carry it around for anchors as a cordalette? Best tied in a big loop or with a small loop on each end? Is it good for prussiks? tethers? tag line?

Last I heard Kevlar crumbles when folded back and forth. It was sold as cord for hexes about a decade ago and then abandoned because it didn't hold up. Mabye this is something new? Otherwise, I'd stay away.

DannyUncanny wrote:The local gym has Sterling Powercord on a spool. I think that a single strand is rated to something huge like 17 kN. Does anybody use this stuff? What are your opinions on it? Worth the extra cost over nylon? Is it only good for tying hexes, or do you carry it around for anchors as a cordalette? Best tied in a big loop or with a small loop on each end? Is it good for prussiks? tethers? tag line?

Sterling PowerCORD

Used it for years, it makes a nice compact cordelette. I stopped using it when I stopped building anchors with a cordelette. It seems, at least to me, that suggestions for a more dynamic anchor have seen a revival over the last few years.

T. Maino wrote:Last I heard Kevlar crumbles when folded back and forth.

This is completely 100% true. Just like everything else you read on this site.

Pretty much only good for tying hexes and specialty uses. Most of the high tech cords are too stiff and static for use in anchors and prussics. The extra strength doesn't really help much, since in the vast majority of climbing uses for cord, you are using it in at least one loop.

T. Maino wrote:Last I heard Kevlar crumbles when folded back and forth. It was sold as cord for hexes about a decade ago and then abandoned because it didn't hold up. Mabye this is something new? Otherwise, I'd stay away.

Well it's a good thing this isn't Kevlar cord then.

Technora is more durable than Kevlar, which is probably why it's used instead of Kevlar (or DuPont doesn't want to be associated with climbers, but the previous guess is probably more likely). Technora has a much higher resistance to flexural fatigue

Technora properties

I use the 5mm Titan cord on my hexes and my lightweight Cord-o-lette. I really like it. It is kinds stiff (compared to regular cord) but its super strong. I use it in just 1 big loop. I think it would make for a nice haul line IF 1) you want to use a static haul line (there are pro's and con's for using both static or dynamic for hauling) 2) are prepared to haul that thin of a line and have a device that can capture your progress effectively. Have not tried prussiking with it but it has a regular nylon sheath so it is not much slicker than most cord (it is a really tight weave though which makes it a bit slick at first) but it is stiffer, IDK how that would affect performance. Hope that helps.

Where Kevlar and Technora cord really is useful is for threads on typical Mediterannean limestone which are unbelievably sharp, so much so that in Italian guidebooks they tell you to carry Kevlar for this very purpose.

I have a Kevlar (or some aramid fiber) pull cord that is 6mm that I have used a bunch. Really like it. Never seem much in the way of brittleness with regard to flexing. I remember that stuff they had out for a while that was used briefly to sling hexes or cams that was supposedly brittle (1990 or so? I think its in an old Chouinard catalot or one of the first BD ones). My rope seems a bit different.

My rope has great hand, soft, supple. I've rappelled on it a fair bit too. Super durable. I'd be more worried about it eating through a biner or ATC than getting cut by most rocks while on rappel.

Not sure I'd car for a chunk of it as an anchor cord, though. Just doesn't absorb shock as well as nylon.

I use a loop of it as a cordalette and it's nice because it's compact. Some things to keep in mind:

- If you're tying it into a loop, you need to use at least a triple fisherman knot (double check me, but I believe this is a manufacturer recommendation)

- Get it cut to the length you want. There's something special about how this stuff is cut which makes it hard to do yourself (I can't find the literature that came with the cord I bought)

- It's stiff enough that once you have more than a couple of clove hitches in an anchor system it starts to kink.

A friend of mine disparages it as "sailboat cord" and says that it deteriorates more quickly than nylon, but I haven't found evidence to support that idea.

Chris D wrote:I use a loop of it as a cordalette and it's nice because it's compact. Some things to keep in mind: - If you're tying it into a loop, you need to use at least a triple fisherman knot (double check me, but I believe this is a manufacturer recommendation) - Get it cut to the length you want. There's something special about how this stuff is cut which makes it hard to do yourself (I can't find the literature that came with the cord I bought) - It's stiff enough that once you have more than a couple of clove hitches in an anchor system it starts to kink. A friend of mine disparages it as "sailboat cord" and says that it deteriorates more quickly than nylon, but I haven't found evidence to support that idea.

Cut it to length with a new/sharp razor blade on a flat surface like a cutting board. No issues at all.

-sp wrote: Cut it to length with a new/sharp razor blade on a flat surface like a cutting board. No issues at all.

Since the core isn't nylon, to keep it from fraying you need to pull the sheath over the core and melt the sheath together so the core is kept inside the now closed sheath.

Bud Martin wrote: Since the core isn't nylon, to keep it from fraying you need to pull the sheath over the core and melt the sheath together so the core is kept inside the now closed sheath.

Yup, was going to type a a whole bunch about pushing the sheath back and then cutting off a bit more then pulling it back and melting the end. Figured it would somehow lead to an argument about sheath slippage or whatever.

jcurl wrote:Am I going to die?

Absolutely.

Yarp wrote: This is completely 100% true. Just like everything else you read on this site.

Actually Yarp, what he is saying does have some merit. Bending cycles do actually make a big difference with some of the more stiff, skinny, and initially strong cords. Sterling Vectran was the precursor to PowerCord and it was really strong when new, but its strength rapidly deteriorated over the course of many bending cycles (i.e. tying and untying the cord in an anchor situation). For this reason, I have switched to using plain old Sterling nylon 7mm cord. It is nearly as strong as the 5.5 mm powercords, but it loses almost no strength over many bending cycles.

Here are some excerpts of actual numbers and a brief conclusion statement from a study that was done maybe 8 years ago or so:

mountainproject.com/v/10656…

mountainproject.com/v/10656…

mountainproject.com/v/10656…

FWIW, I've played with this sort of stuff more than most people and have more than a few comments:

1. Thought I saw a comment above re: "sailing cord", but don't see it now. Regardless, that comment isn't entirely misplaced.... Many of the high strength cords on the (non-climbing) market are ill-suited to climbing use and behave badly when used in climbing applications. Two cases that come to mind are double braid PoBOn/Zylon and Technora, which IIRC in my pull testing had the sheath strip followed by unpleasant things happen to the core when knotted (spliced eye on one end, clove hitch on the other). Quite simply these sorts of cords aren't made for knotting and while spliced ends are fine they do _bad_ things when knotted.

2.During these pull tests versions using a Dyneema/Spectra or Vectran core faired better than PoBOn/Technora, but only because the non-aramid core didn't shred as the sheath pulled along it after failure. A vectran core seemed to fair better with a clove than dyneema, but neither were particularly faith-inspiring when loaded as the sheath would strip well before core failure (which means knotting is a major issue, with the vectan holding the sheath marginally better than the dyneema). Sure, the core failed at a higher number than what's commonly used in perlon, but the perlon didn't have the sheath fail and thereby render the cord unusable. That said, I'm not sure the differences I saw between Vectran and Dyneema/Sprectra are due to the fibers themselves or the urethane coatings applied to the cores. The coating thickness seemed to vary between manufacturers and seemed to have an effect on how readily the nylon sheath stripped.

3. Some tech cords have woven cores and others non-woven. Not much a difference as far as I can tell, unless you know how to do a spliced double braid eye. Reason I mention it is that it can potentially give you a high strength rabbit-runner without the bulk of webbing. Then again, I've found the issues with stripping of the sheath disconcerting in this configuration and can't recommend it beyond poking at in a lab setting. YMMV.

4. Long story short- slinging hexes/etc = ok/encouraged. Most everything else, do some research and come to your own conclusion. Some will say it's fine for anchors, others will say you're gonna die. Use your head and climb safe.

-a.

If the powercord you are referring to is 5.9mm powercord, then it is great for anchors and descent for prussics. Sterling also recommends it as a great tag line. It is a nylon sheath and technora core. I love them as cordolettes for anchors.

I've got some Kevcord' on my BigBro's, and a loop or two for misc. use on anchors or as a backup because it's light and strong. Does kink up when folded up though...have heard that's not good but only if it's actively stressed , kinked and unkinked during use I thought.

Woodchuck ATC wrote:I've got some Kevcord' on my BigBro's, and a loop or two for misc. use on anchors or as a backup because it's light and strong. Does kink up when folded up though...have heard that's not good but only if it's actively stressed , kinked and unkinked during use I thought.

Kevlar is an abrasive material that wears through itself with repeated loading. As you bend the material over and over, the strands start to break down, which we refer to as flex fatigue. Kevlar is amongst the oldest high strength fibers and it is not very popular anymore both because it suffers from flex fatigue and because it cannot withstand sunlight without experiencing some strength reduction (or any UV for that matter). Nowadays manufacturers and engineers can choose from a number of fabrics, each with their own drawbacks and positives. UHMWPE (Dyneema and Spectra) is amongst the best and most popular high-tech fibers used today. Other options include nylon, PET (polyester), PEN (Pentex), PES (different polyester), PBO (Zylon),Vectran (liquid crystal) and a few others. Nylon is the most stable material, but it is also the weakest, except for polyester which is apparently stronger pound for pound, but not in surface area.

Jim Titt wrote:Where Kevlar and Technora cord really is useful is for threads on typical Mediterannean limestone which are unbelievably sharp, so much so that in Italian guidebooks they tell you to carry Kevlar for this very purpose.

That's why I'm in this thread ha! Trying to figure what my Sicily guide book means by kevlar threads. The rock here DOES get sharp! The two-finger pockets can be a nightmare!

Why not just regular old 6mm nylon (perlon)? Single strand breaking strength is over 7kN. In just a simple loop, you're up at 14kN. Two piece pre-equalized anchor = 28kN (less for bad equalization down to 14kN worst-case). Three piece = 42kN (again, down to 14kN). Strong enough for me.

Beyond that, it's slightly dynamic, which makes it a lot less likely you'll ever see those forces.

And it's cheap.

Even for reslinging gear, 14kN is stronger than most gear.

What am I missing?