Should I be using Dyneema slings for lead climbing anchors?
I've seen a few of these comparisons around but I've always struggled to make sense of them.
At the moment I do quite a lot of Alpine style routes (lowish grade (HS), long multi pitch routes, typically up arete's etc) in Snowdonia. These routes typically have lot's and lot's of spikes. So I tend to use these spikes as lead anchors as I move up. At the moment most of my slings are Dyneema slings. It occurred to me the other day that maybe this wasn't a great combination?
Given the low stretch properties of Dyneema. Should I be using these as lead anchors over flakes or should I switch to nylon?
Presume the flake will take a the impact.
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Either will work, but Dyneema and Nylon have different properties that can make them more or less advantageous in certain situations.
Dyneema is obviously a lot lighter than nylon, which gives it a lot of it's appeal for alpine climbers, it is also more abrasion resistant, in fact the material is also used to make cut-resistant gloves. The disadvantage to dyneema is it's low melting point (which is partly why it fails so easily when knotted), and that it's too slick to hold knots very well, which means dyneema typically always has to be stitched.
Nylon is preferable to dyneema in many situations because it does have some stretch, as well as a higher melting point, but it is a lot heavier, and less abrasion resistant. Another advantage that nylon has over dyneema is that it can be easily tied, very useful for anchoring around trees, in natural threads on rock, and vthreads on ice. If you only had stitched dyneema slings, you'd have to cut one to thread it, and you'd have a very tough time tying a knot in it that would hold.
In your situation (placing slings over flakes) I would suggest using dyneema slings, as they would be more resistant to being cut by a sharp flake in the event of a fall, just don't tie any knots in them.
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See: Slings for anchoring and lanyard in rock climbing
Different question, but but it contains a lot of the same releveant information for an answer to this one also; basically either one will work well.
Short summary: Your rope is designed to absorb the impact of your fall, while a sling is absolutely 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. There might be some marginal decrease to impact force on your protection (namely spikes in this case) by using Nylon slings, but it's rarely going to be a measurable difference.
A good and attentive belay, and a soft catch is your best defense from high impact forces, and any UIAA approved sling can be expected to hold the force of a falling climber when being belayed by a rope.
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Given the low stretch properties of Dyneema. Should I be using these as lead anchors over flakes or should I switch to nylon?
Yes, it's absolutely fine. Whichever sling you use, your rope is the dynamic (shock-absorbing) part of the system, and that doesn't change.
You shouldn't clip directly into either, and Raz's linked answer covers most considerations for choosing between them.
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