Sling Materials Explained

You’ve seen all the sling choices and aren’t sure: Dyneema, Spectra, Dynex or Nylon. This post dives quickly into the pro’s and con’s along with the best uses and the rest of the post is dedicated to explaining exactly why we’ve labeled them as such.

Overview: Nylon vs Dyneema

 

NYLON

Pros

• cheaper
• colorful
• stretchier (more dynamic during falls = less impact)
• easier to untie [weighted] knots
• can buy in any length from spools

Cons

• bulkier
• heavier

Best Use

• anchors
• sport quickdraws
• repetitive fall situations

 

DYNEEMA

Pros

• higher strength to weight ratio
• absorbs less water
• easier to rack/extend
• lighter, thinner, more pliable
• more abrasion resistant
• more resistant to UV rays
• easier to rack/extend

Cons

• expensive
• minimal stretch to reduce fall impact
• lower melting point
• knots reduce strength
• knots are difficult to untie

Best Use

• alpine draws
• when weight/low bulk really matters

 

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Getting Into The Details

 

Nylon

Nylon is the original sling material. It actually took quite awhile to become adopted into climbing practice and it wasn’t until the late 60’s and early 70’s that it became universally accepted (thanks to Outdoor Gear Labs for the history).

PROS

The most significant benefit of using nylon instead of Dyneema is that it stretches when weighted, reducing impact forces on you and your gear. Rock and Ice reported, In a fall, nylon stretches up to 30 percent, thereby dynamically absorbing the energy of a plummeting climber. [Dyneema] stretches a scant three to five percent.

Nylon slings are also much less expensive at roughly half the cost of Dyneema.

Nylon is also super colorful. You can color code each length of your nylon slings so it’s easy to see what’s on your rack. And, if you take a beginning mountaineering course, and everybody is using wide nylon, there’s often enough color options to tell your sling apart from others.

When Black Diamond’s Quality Control guru, Kolin “KP” Powick, tested a plethora of dogbones found at crags, he found that the nylon slings were the strongest. Although the test wasn’t the most scientific (samples were taken from many areas and did not incur exactly the same use), it did show that their is a wide variance of what “old” slings will hold before breaking, and nylon always seemed to come out on top.

CONS

The negatives of nylon are quick and simple to explain: it’s bulkier and heavier. To achieve the UIAA-required minimum strength of 22 kN, nylon is roughly double the width and weight of equivalently certified Dyneema.

If you’re an ice climber or mountaineer, it’s also worth noting that nylon can absorb a lot more water, which means added weight and the tendency to freeze more quickly.

SPOOLS AND KNOTS

Spools of nylon are readily available at most outdoor stores, and can even be ordered online. This means you can choose your ideal length and tie your own slings. In addition to choosing any size you want, it also increases versatility as you can untie the sling and tie it around features such as trees, chockstones, etc. while using it for protection during the climb or while securing an anchor.

Since nylon is wide, and not particularly slippery, it is also easier to untie weighted knots.

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Dyneema, Dynex and Spectra

WHAT IS IT

Dyneema, Dynex and Spectra are all brand names for “Ultra High Molecular weight Polyethylene” (UHMwPE) and are essentially the same thing. Note: Since they are not 100% the same in their properties, we list them separately as filters on WeighMyRack because some climbers state a preference (we don’t). From this point on I’m just going to use Dyneema to refer to all 3 materials because it’s the most common name used in the climbing community.

PROS

Dyneema is impressive because it has a much higher strength to weight ratio than Nylon. Mammut reports a tensile strength roughly 15 times greater than steel and 40% greater than aramid (Kevlar) by weight [pdf]. This allows Dyneema to be about half the weight and width of nylon.

Dyneema is much thinner, lighter, and far more packable and pliable than nylon. For alpine draws in particular, Dyneema is easier to rack and extend because of their small, skinny and flexible nature.

Here are two examples of alpine draws (and you can read more about tying alpine draws and other benefits on Climbing.com):

Dyneema is also more resistant to UV damage and abrasion. Although, as we referenced earlier with the BD QC Lab study, this UV resistance may not significantly impact strength in real-world climbing situations.

Because of Dyneema’s super tight weave, it absorbs less water, and it even floats. Since it absorbs significantly less water, it’s ideal for ice climbing and mountaineering as the sling will be much less apt to freeze than nylon.

DMM has done extensive testing and quite interestingly they found particularly for the 8 mm tape, the breaking strength [of Dyneema] increased if the Dyneema® was wet or frozen. This is very likely because the water facilitated heat transfer, reducing heat build up along with a slight lubricating effect. It is possible to see steam coming from some of the wet slings as they are being loaded.

CONS

For most climbers the most significant disadvantage of Dyneema is the higher cost.

That being said, it’s important to note Dyneema’s lack of stretch in a shock-loading situation. When taking a fall, there is a much harsher impact to the gear you’ve clipped and on your body due to the lack of give (3-5% stretch versus nylon’s 30%). This also means if you use Dyneema in your anchor, you should be ever-so-vigilant to make sure it is taught at all times, as even a short fall can severely shock-load the system.

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FURTHER

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This would be a great time to head over to the DMM blog and see their studies (video/write-up/graphs) of falling on Dyneema/Nylon to see where and when it breaks. DMM describes how even a 60 cm fall-factor 1 fall on to an open Dyneema® sling can generate enough impact force (16.7 kN) at the anchor to pull a Wallnut 11 wire (12 kN) apart.

In an ideal world, your rope handles the dynamic stretch during a fall and you don’t have to worry about Dyneema’s lack of give, as one should never take a direct fall on the anchor. However, climbing isn’t always text-book perfect. For example, the anchors might not be in the direct line of the climb when your partner yanks you in a different direction. Anyone ever scootch above their anchor to deal with a cluster? With all of the potential scenarios, stretchier nylon is the safer anchor bet.
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Additionally, Dyneema has a lower melting point, ~145°C, compared to Nylon (245°C). We all know rope on webbing contact should be avoided, but this means it’s even more critical to avoid with Dyneema.

SPOOLS AND KNOTS

Dyneema isn’t readily available in spools. Since Dyneema has a lower coefficient of friction (it’s more slippery), which is great for abrasion resistance, it also means if you are ever tying your own Dyneema strand (instead of using a sewn-sling) you must leave extra long tails, because the knot can be expected to slip and potentially unravel when loaded. This is extra important to note if you’re only carrying Dyneema and need to cut one and re-retie for a rappel or as a heads up if you were planning to buy larger Dyneema slings with the intent of cutting them to smaller sizes.

This slippage also means Dyneema knots can become particularly tight, sometimes leaving heavily weighted knots virtually impossible to untie. In general, knotting Dyneema is not a good idea as it drastically lowers its strength. Mammut did an in-depth study on how slings break, particularly those girth-hitched, and concluded:

All climbers should be aware that girth hitching any Dyneema slings, regardless of size, causes them to lose around 50% of their strength… [B]ased on the fact that a UIAA certified sling holds at least 22kn (roughly 5000lbs), when girth hitched 880DaN or 2000lbs strength should remain. With normal human weight and under the described circumstances, this force could only [be] reached with a multi-meter drop.

Girth hitches aren’t the only knot that reduces strength significantly, all knots do (a triple fisherman’s reduces strength the least). Read more details about knotting Dyneema on DMM’s blog (they have a video, graphed results, and a great summary write-up).

Although there are some notable disadvantages to Dyneema, most of them can be overcome by being thoughtful and careful about your gear and the situations the gear is used.

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WEIGHT COMPARISONS

Dyneema is smaller and lighter. But how much so? For 60 cm sling offerings, the width and weight ranges are such:

	Nylon	Dyneema
Width Range	16 – 19 mm	7 – 13 mm
Weight Range	27 – 48 grams	16 – 30 grams

If your rack was made of twelve 60 cm slings the min weight and max weight would be:

	Nylon	Dyneema	Difference
Min Width	324 grams	192 grams	51%
Max Width	576 grams	360 grams	46%

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Hybrids

All Dyneema slings have a small amount of nylon blended in. Nylon makes up the colored section of the sling and is most often seen on the outer edge of the sling (Dyneema cannot be dyed so that part will always be white). Yates states that the nylon edge acts to protect the Dyneema fibers from snagging on crystals and “pulling” from the webbing.

Today, there are hybrid Dyneema/nylon slings that have more equal amounts of each material. For example, Metolius Open Slings are 40% Dyneema 60% nylon. A visual inspection of Omega Pacific slings shows they have a similar split.

These hybrid slings may offer benefits of both materials – less expensive than Dyneema slings while still being fairly slim and strong.

Polyester

We’re not sure the exact material composition of the polyester that Mammut, Petzl, and Fixe use for their slings (the only brands to list polyester as the material type). But both polyester and Dyneema are polyethylene-based: polyester is polyethylene naphthalate while Dyneema is UHMwPolyethylene.

Internet research will tell you that polyester is softer, somewhat more durable, and a little stronger than nylon. Like Dyneema, polyester is resistant to stretching (3%) and shrinking and it is more UV resistant and abrasion resistant than nylon and it repels water. But, polyester has a more similar strength-to-weight ratio to nylon.

According to Dave Savage, an Industrial Yarn Specialist, polyester is what Europe’s uses instead of nylon. He wrote a blog post on Service Thread that talked about sling material (slings in general, not just climbing slings) and said:

Historically in the sling industry, the US market has been 80 to 90 percent nylon, using polyester where it was essential for UV or chemical resistance. The European market is the exact opposite—they have historically used upward of 90% polyester webbing for slings.

That article also add that polyester is getting cheaper and nylon is getting more expensive. That said, it’ll be curious to see if the number of polyester slings continues to increase.

 

Summary

Dyneema is great for alpine/trad draws (extendable slings), and nylon is ideal for sport draws seeing lots of use and projecting, as well as anchor systems.

When buying quickdraws for sport climbing the majority of the options have nylon slings. There are lightweight quickdraws available with Dyneema dogbones that are totally legitimate too but they are more expensive. Unless you’re projecting from the ground up at your limit, or simul-climbing with 20+ draws, most climbers will find the cost of Dyneema draws outweigh the weight and size advantages (unless you find a great sale, in which case, no need to hesitate).

While alpine climbing, when weight reduction is a major goal, Dyneema is used for the majority of quickdraws, alpine draws and slings (this lightweight trend is only increasing). Most alpine climbers will still take some tied nylon slings and/or prusik cord because they are the most versatile option for anchoring and securing the rappel. Nylon, along with prusik cord, is the best choice for rap anchors as it is the easiest to sling trees, boulders, and whatever else your anchor includes.

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