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How to Climb Safe: Spectra versus Nylon

09-Jan-2013
By Rob Coppolillo

Cody Simms flight testing slingage on the Gunks&#39; <em>Twilight Zone</em> (5.13b). Photo by <a target="_blank" href="http://www.jimthornburg.com/">Jim Thornburg</a> Britney or Christina, Frappuccino or half-caf vanilla latte, Maxim or FHM, trad or sport—our world is full of crucial, life-defining choices. While we’ll bicker endlessly about the various merits of pop divas, Yuppie café beverages, softcore skin rags or climbing disciplines, when it comes to picking slings, we fall back on instinct or laziness, either snagging what’s cheap (nylon), or strong and light (Spectra). Your sling choice, however, truly is life affecting. Read on to find out why.

WHAT’S THE DIFFERENCE?

Nylon, which appeared in the 1930s, was immediately hailed as a miracle fiber. This wonder thread had a theretofore unseen strength-to-weight ratio that beat even spider silk. What’s more, the petroleum-based product was cheap and easy to manufacture and stretched like a Cirque du Soleil acrobat. It was thus the perfect choice for women’s panty hose—and for climbing ropes and slings, trumping the wimpy, heavy hemp and cotton used by vertical adventurers from Whymper to Mallory to mountain troops of the pre-WWII era.

All was gnosh until the mid-1980s, when geeky, white-suited lab rats devised another petroleum product, Spectra (aka Dyneema), a high-density version of polyethylene. This textile, though costing three times more than nylon, is also three times stronger for its weight, absorbs less water than nylon and practically requires a chop saw to cut. It became the hot ticket for products from bulletproof vests to sails, and found converts in the climbing world, where featherweight Spectra slings (half the heft and bulk of nylon) and daisy chains became all the rage.
By now, you’re probably ready to pawn your Spectra slings on eBay. Mistake. In the field, both Spectra and nylon perform well. Choosing between the two, as we’ll see below, isn’t an all-or-nothing proposition. With no documented instance of a Spectra sling failing in a real-world situation, there are even certain functions where it is superior to nylon.

But not so fast. In a fall, nylon stretches up to 30 percent, thereby dynamically absorbing the energy of a plummeting climber. Spectra stretches a scant three to five percent. “[Spectra is] nice if you’re using a daisy chain that you don’t want to stretch,” says John Yates of Yates Gear, but a fall on that daisy or sling is “literally like falling onto a cable.”

Problem 1: In tests, Spectra daisy chains and slings have snapped in relatively short, static drops, such as the type you’d take if you fell directly onto a daisy or a sling clipped from a piece to your harness. The breakage occurs for two related reasons. First, Spectra does not, for all practical purposes, stretch. Second, Spectra melts at a temperature 100 degrees lower than that of nylon. Since Spectra cannot stretch to gradually decelerate a falling object, the force of a fall almost instantaneously generates a tremendous amount of heat (energy), which in turn damages the material, causing it to fail. For this reason, think twice before using Spectra in static-loading situations.

Problem 2: Spectra is much slicker than nylon. Knots tied in Spectra tend to unravel or pull through themselves under load. Spectra’s inability to hold a knot is one reason why Spectra webbing typically isn’t sold off the spool at climbing shops and comes only in finished, sewn products. The exception is Spectra cord, which you can purchase in raw lengths. If you use Spectra cord, read the next section very carefully: Tests conducted by Yates show that 14mm Spectra slings containing 50 percent nylon (Spectra slings and cords use nylon as “filler”) and rated to 5,600 pounds pulled through themselves at 3,660 pounds of force when tied with a water knot. Double and triple fisherman’s bends proved much stronger. While Yates only tested webbing, the lesson learned also applies to cord, which, if anything, due to its roundness is even more likely to work itself loose. If you use Spectra cord or are in a situation where you must cut and retie your sewn Spectra slings, such as threading an hourglass or backing up a snarled-mass-of-webbing anchor, use a triple fisherman’s bend. Leave tails long enough to finish with a single fisherman’s bend.

Spectra’s slipperiness has another drawback: Weighted knots can tighten such that they’re almost, or even literally, impossible to untie. Though advantageous for slings, this syndrome snarls up cordelettes and webolettes, which you re-rig, tie and then untie at every belay.

Problem 3: Finally, Spectra doesn’t resist the degradation caused by flexing as well as nylon does. The repeated bending action of a Spectra sling through a cam stem, for example, breaks down the textile fibers more quickly than nylon ones. For this reason, Bill Belcourt of Black Diamond recommends replacing Spectra runners and cam slings more frequently than nylon ones, “especially if you’re using them hard.”

By now, you’re probably ready to pawn your Spectra slings on eBay. Mistake. In the field, both Spectra and nylon perform well. Choosing between the two, as we’ll see below, isn’t an all-or-nothing proposition. With no documented instance of a Spectra sling failing in a real-world situation, there are even certain functions where it is superior to nylon.

==


IT'S A HARD-KNOCK LIFE

Here are some guidelines, drawn from common climbing situations, to help you choose between the two materials and decide when and how to use each. Remember, these are just guidelines: Let common sense and experience dictate your decision-making.

As a general rule, don’t use Spectra in situations where the sling or daisy chain alone must hold a fall, or when there’s very little rope in the system. Examples include:

As a general rule, don’t use Spectra in situations where the sling or daisy chain alone must hold a fall, or when there’s very little rope in the system.

1. Daisy-chain fall: If you connect yourself to a nearby piece, usually an aid placement, with the daisy chain rather than the rope, and pitch, the fall factor (length of fall divided by the amount of rope catching the fall) generates tremendous forces that can rip or break placements. Worse, these types of falls can cause internal injuries. John Dill, head of YOSAR, reports that he’s “seen injuries out there, busted ribs, guys sore for days” after taking daisy-chain falls. Adds Yates, Spectra daisy chains for aid climbers, “are not a good idea.” A nylon daisy is the preferred tool, but still is not recommended for catching falls. Your best bet is to hone your aid technique such that you’ll never again lead above a daisy chain—Spectra or nylon—clipped to a low piece.

2. Fall onto the first piece of pro: As in a daisy-chain fall, when you drop onto the first piece of gear—a common scenario on multi-pitch routes—you hit hard because there’s little rope in the system to elongate, and decelerate your fall. To soften the blow, use a nylon runner on your first piece. Though nylon stretches ever so slightly, at least it stretches some. (Also, use a fresh rope with a low impact-force rating, which will keep forces even lower.) As you climb past that first piece and introduce more rope into the system, thereby lowering the fall factor,  you can runner-up the rest of the pitch with light and tidy Spectra.

3. Fall onto a sling girth-hitched to your harness: Another common mistake, this happens when you girth-hitch a sling to your belay loop and clip the sling to a placement to hang and rest, or to temporarily anchor yourself independent of the rope. Then, you either slip and fall onto the sling, or resume climbing, forgetting to unclip ... and lob. Again, the fall factor—and forces—are extremely high. Use a nylon sling instead of a Spectra one as your impromptu “daisy.”

4. Cordelette (or webolette) fall: This happens when a cordelette goes slack, usually because your belayer is fishing a bagel out of the haulbag or generally dicking around when he suddenly slips and hammers directly onto the anchor. While both a nylon and Spectra cordelette are shock-loaded here, the nylon will stretch and dissipate energy, even if only a little, reducing the impact force and helping equalize the cordelette. A static, Spectra cordelette transmits higher forces to the anchors; unless the cordelette is perfectly equalized, it will load one placement more than the others. Bad juju.

IN A PERFECT WORLD...

Besides having certain advantages for cordelettes, daisy chains and runners, nylon remains the best material for rigging rappels. Nylon webbing is cheap and easy to buy in bulk, holds knots, readily cuts to length and doesn’t melt as quickly as Spectra—a plus in those dicey situations when you’re sans rap rings or carabiners and must thread the rope directly through the sling.

On the other hand, Spectra runners are so streamlined and superlight you can carry nearly twice the number for the nylon equivalents. Spectra also has a decisive edge in ice and alpine climbing, and mountaineering. In these cold, wet pursuits, nylon slings can freeze stiff and become as unusable as your popsicled fingers. Spectra, because it absorbs less water, remains more pliable.
In the final analysis neither nylon nor Spectra is perfect. As Belcourt says, “Spectra and nylon are both good materials. You just have to use them the right way.” In short, carry a mix of slings, using nylon when its advantages shine, and Spectra when appropriate. Buy wisely, climb smart and save your mental energy to help solve the ever-vexing Britney-versus-Christina dilemma.    

Spectra Do’s and Don’ts

Don’t
● Use a Spectra sling as an
impromptu “daisy chain.”
● Lead above a Spectra  (or nylon) daisy chain clipped to a piece below you.
● Use knotted Spectra slings.
Do
● Frequently check Spectra slings, including those on your cams, for wear.
● Use a triple fisherman’s knot to tie Spectra cord.

Nylon Versus Spectra

Nylon Pros
● Relatively inexpensive
● Stretches
● Holds knots  
● Higher melting point than Spectra
● Holds up to repeated flexing better than Spectra      
● Great “all-around” material

Nylon Cons
● Absorbs more water
● Susceptible to UV
    degradation
● Heavier and bulkier
    than Spectra

Spectra Pros
● Three times stronger by weight than nylon
● Very lightweight
● Low bulk  
● Absorbs little to no water   
● Highly abrasion- and
    cut-resistant

 Spectra cons
● Doesn’t stretch
● Doesn’t hold knots
● Expensive
● Low melting point
 

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