Probably common question, but: What slings do you use to build anchors for belaying the 2nd in rock climbing? Dyneema or nylon?

I had discussed this problem with my friend and he said that Dyneema is better as it has greater strength ratio and other characteristics (but it's not important).

As I know and had remain DMM's tests (HOW TO BREAK NYLON & DYNEEMA® SLINGS and SLINGS AT ANCHORS [VID]), nylon has better fall absorption, so, I would use these slings on anchors and lanyard when belaying.

  • Funny, I was going to open this topic at some time too because I saw this DMM video couple of weeks ago. I found it very informative. Great question and we already have an absolute quality answer. Thx guys!
    – Wills
    Commented Nov 24, 2014 at 22:02
  • 3
    The DMM links are really good, and surprised me about a lot of things. I didn't know that it was possible to break a knotted, shoulder-length sling with a fall-factor-1 fall equal to the length of the sling -- scary!
    – user2169
    Commented Nov 25, 2014 at 1:35
  • Related: supertopo.com/climbers-forum/2542038/… The video is in French, which I understood only a little of, but the accompanying discussion seems to say that knotted dyneema can fail under a fall factor as low as 0.3.
    – user2169
    Commented Dec 9, 2014 at 3:30

1 Answer 1


While both materials do have slightly different properties, either one will work in the scenario mentioned. In-fact, any sling with the UIAA stamp of approval will likely have a working strength of 22kn - more force than you will ever be able to generate by falling if being belayed by a rope.

The latter part is important, because the rope (among other things) is what will absorb the energy of your fall in this scenario, not the sling. Again, just to elaborate: Your rope is designed to catch the impact of your fall, a sling is not. In the videos presented by DMM you can see what happens when the sling is forced to absorb the impact of a fall, and it's not pretty.

The question of what material to choose from will depend on the conditions more than anything else. Materials like Dyneema are lighter, and won't absorb as much water as Nylon in wet weather, making them the ideal choice for applications where weight or weather is a primary concern, like mountaineering for example. They also have the lowest melting point from all the climbing fabrics though, so will probably need replacing sooner.

On the other hand, Aramids (Technora, Kevlar etc..) can be just as strong, and have the highest melting point of most materials, upwards of 500C celcius. This makes them perfect for those long rappels, or hauling and rescue scenarios like firefighting. They also happen to have a much worse shelf life when it comes to UV degradation (from exposure to the sun) however. Nylons fall somewhere in between on both counts.

Ultimately, any UIAA approved sling can be expected to hold the force of a falling second when being belayed by a rope; and if switching leads, you can always use the climbing rope itself to tie an anchor also.

Climbing Rope Anchor

Here is a link to the properties of some common materials as further reading: http://www.marlowropes.com/technical/physical-properties.html

Beyond material properties, additional preferences will come from application, and which fabric will be easier to work with. For example, knots are easier to untie from thicker material, so Nylon will be a better choice if you are putting in lots of knots.

  • Great answer, thank you. Can I ask You another question? What do you think about build an anchor on I beam with nylon or dyneema sling instead of heavy duty anchors? Of course, edges should be protected.
    – dhpasta
    Commented Nov 24, 2014 at 22:02
  • I shy away from recommending specific gear, but I'd personally want a beefy nylon sling for that application. Something similar to this: mec.ca/product/5031-581
    – Raz Peel
    Commented Nov 25, 2014 at 3:38
  • Can You shortly tell why nylon one, not other? I think that this one, as has better energy absorbtion during fall and in such a situation weight and size don't matter. Also when using edge protection unbrekable abilities of Dyneema and heavy duty slings are not require
    – dhpasta
    Commented Nov 25, 2014 at 6:19
  • It will be a LOT easier to untie after repeatedly weighing your anchor if you used a thick nylon sling rather than a skinny dyneema one (or similar). Truthfully, if weight and size don't matter at all. Get one of the nylon cables they use for Rope Access work like this: cdn.simplifiedsafety.com.s3.amazonaws.com/images/…
    – Raz Peel
    Commented Nov 25, 2014 at 15:53

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