I’ve been looking to upgrade my cordalette to something a little lighter (always been instructed to use 7mm cord but have always hated the weight and bulk) and am quite confused. Some say a straight up 5mm cord is fine, other say if you want to go that thin it should be the 5.5mm titan dyneema cord, other say just moving to a long spectra or dyneema sling would be best. I’d love to get your opinion/hear what you use.
Great question! Generally, I don’t use cordelettes, because I don’t like to carry the extra weight. I will use them if I am doing rigging work, and occasionally for big wall use where going light isn’t as big of a deal and it’s worth the trade off in weight for a simple, accessible anchor point. On long routes, I usually keep a light daisy chain girthed to my harness. I use this daisy chain as a preliminary clip in-point while I set up my anchor, which I do with 2 ultralight locking carabiners and a bunny-ears knot made of the climbing rope that I am directly tied into. I know you are probably going, “a WHAT knot?” I will do a post on that knot before too long, I promise.
To answer your question, I checked in with Dave Furman, the hardgoods manager at Mammut and my gear-expert friend. He wrote some great guest posts here already about differences between ropes, and he knows a lot about specs and the more technical capabilities of cordage. Here’s what Dave has to say about cordelettes and rope diameters:
People should remember that KN are a measure of force, which is determined not only by the mass of the object lobbing off a cliff, but by the acceleration of the object—in this case a climber. It is very easy for an average-sized climber to generate a lot of force during a fall, especially in circumstances that can cause the belay anchor to be loaded—because we only have one belay anchor in question, no matter the material we should strive to use anchors that are redundant (i.e. if one element fails there is always a backup—this includes the anchoring material), and to protect the anchor by placing protection and by building dynamic elements into the anchor (such as tying into the anchor with your climbing rope rather than clipping directly to a sling or cordellette). These practices are just part of building good anchors and should be a given no matter what the anchor material is.
No anchor-building material is perfect, all of them having tradeoffs between strength, weight, bulk, durability, dynamic properties and versatility. Mammut’s 5 mm accessory cord has a breaking strength of 5.5kn (about 1200lb), 6mm is 7.5kn (about 1700lb) and 7mm 13kn (about 2900lb). Note that the 7mm cord is over 40% stronger than the 6mm, and almost 60% stronger than 5mm. A permanent loop sling such as our 8mm Contact in the “cordellette” length of 240cm is low in weight and bulk, quite strong (22kn, or about 5000lb) but it cant easily be un-knotted for other uses and being much less stretchy than nylon it is important to always use the dynamic climbing rope to tie-in to a belay constructed from this material in order to have some “give” in the anchor. In addition, since any knot will weaken a material, these slings don’t necessarily need to be weakened with a knot in order to build an anchor. Tech cords are pretty low in bulk and can be pretty strong, but many of them have been shown to suffer decreased strength from repeated bending—essentially the knot always in the same place can cause them to fatigue much like a metal does when bent back and forth repeatedly at the same point, so they have a limited lifespan, as well as being essentially static like the Mammut Contact slings. Nylon cord is not as strong—the 5mm size which is most comparable in weight and bulk to a Contact sling or tech cord is far weaker than those alternatives—but it does not fatigue, it is durable, it stretches and provides a dynamic element built right into your belay, and it knots easily and can be used to back up a rappel anchor or make a prussic or other tool in a self-rescue or emergency situation. Climbers should be aware of all of the strengths and weaknesses of all of these materials when choosing between them, and construct their anchors accordingly. Although some climbers may use cord thinner than 7mm for constructing belay anchors, it is important to note just how much stronger the slings and 7mm cord are in comparison, especially when you consider that these are often weakened by knotting them and by concentrated wear at the knots. We definitely do not advise people to use 5 and 6mm cord for anchor construction, and if climbers choose to do so they should be acutely aware that they are putting themselves at extra risk by doing so and take any necessary precautions (frequent wear-checks, being extra conservative in deciding what is worn and discarding it, always placing protection specifically to protect the belay from high impact, using a dynamic belay device and techniques, terrain and belay location choices, etc). A calculated risk may be acceptable to some people if it is truly calculated, but done out of ignorance or by guesswork it is asking for trouble. Because most people aren’t willing or able to objectively test these out for themselves to see what their true level of safety (or lack thereof) is, if a nylon cord is used I’d strongly recommend using 7mm for anchor construction, and if the weight and bulk is a significant problem using a Contact sling with a 22kn breaking strength, remembering to tie into the anchor with the rope.
Hardgoods Category Manager
Mammut Sports Group, USA and Canada