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Behind the Scenes: How Climbing Harnesses Are Designed and Tested

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rock climbing harness Cam Stuart Katie Mah hang test Arc’teryx design testing
Cam Stuart and Katie Mah during a harness hang test at Arc’teryx.Courtesy of Arc’teryx

Our victim—a nameless, limbless dummy—lay suspended, attached at the neck and groin via carabiner, a climbing harness strapped around its waist, while the machine slowly pulled tighter. With their ominous-looking hooks, wheels, and metal appendages, the machines for testing sit harnesses looked like relics from a torture museum. However, they were exactly what one would expect in Arc’teryx’s North Vancouver R&D facility. Here, in late 2017, Bill Burke, a tool and mold maker (offical tester), summed it up well: “It doesn’t seem right to give names to objects [the dummies] you’ll be submitting to grueling testing.”

Before harnesses, climbers would tie in via rope wrapped around their waist or chest; then along came the swami belt, a makeshift webbing harness that eventually saw the addition of leg loops. The first sit harness was sold commercially 50 years ago. However, other than the general “Please keep us safe,” North America does not, unlike with military harnesses or those used in a professional setting (i.e., OSHA standards for harnesses used for window washing, tree work, etc.), have a legislated standard for recreational harnesses. Fortunately, most brands create their harnesses to meet or exceed rules outlined by the European Committee for Standardization (CEN), which let you sell your wares in Europe, and the Union Internationale des Associations d’Alpinisme (UIAA): standards EN 12277 and UIAA 105.

belay loop static resistance test Veronique Guerange Petzl rock climbing harness design
Though this dummy is upside down, the belay loop is still being pulled in the direction of the dummy’s head. Tests like this static resistance test, performed by Veronique Guerange at Petzl, are used to fulfill international standards and for in-house specifications.Courtesy of Petzl

Harnesses undergo two main sets of tests: those conducted in-house on the raw materials and those conducted on the finished product, which include proprietary in-house testing plus the CEN and UIAA standards. For the first volley, suppliers send raw materials to the manufacturers. “Suppliers provide us with a test report .… All incoming materials get verified before moving to production,” says Tom Fayle, director of advanced research and development at Arc’teryx. “They’re quarantined until we’re sure they’ll pass, and additional random testing is conducted throughout the process.” As Pierre Plaze and Jon Rockefeller of Petzl shared, “Catching problems prior to building the harnesses is crucial. Being a life-safety item, you want to know that every element exceeds its minimum requirements.”

The best way to describe the raw-materials area at Arc’teryx is as a wall of fabrics, with colorful cloth spools; reels of webbing, threading, and cord; piles of plastic; and bins of metal bits. Harnesses are composite structures of multiple, layered materials. From tension testing to counting thread, from use trials to visual inspection, design is hands-on—the designers layer, stitch, and combine the materials in novel ways to create prototypes. “Almost everyone in design or development has a sewing machine. We build mock-ups and prototypes all day, every day,” says Katie Mah, an Arc’teryx designer.

15 kN Arc’teryx test UIAA EN standards rock climbing harness design
This harness was fitted snug to the dummy, but nearing the 15 kN of force required by the UIAA and EN standards, things start to get stretched at the Arc’teryx facility north of Vancouver, BC. The harness passed with flying colors.Samantha Sanders

Once you have a prototype, the next step is in-house testing. The tests run the gamut: from finding individual components’ or the prototypes’ breaking strengths (failure testing via pulling, with the occasional drop test), to comfort testing (imagine being suspended while typing on your computer), to comparison studies (like having a gym session in a harness whose left side is completely different from the right). Having survived these, a harness is now ready for the final step: EN and UIAA standards testing.

The EN standard is the baseline and contains two major tests. (The UIAA adds further details, meaning if you meet the UIAA standards, you’ll meet EN standards as well.) The first test, designed to mimic the loads your harness might see in a fall, requires the harness to be fitted normally over the aforementioned dummy. The dummy is fixed in an upright, vertical position by a connection at the neck and one at the bottom. The belay loop is then hooked to a testing machine, which slowly pulls until it’s applied 15 kN of force. It pauses, releases, then starts pulling again to reach 15 kN, before releasing a final time. The harness is checked for slippage of more than 20 mm at the belt or waist-adjusting devices and for damage to structural components.

rock climbing harness testing several-ton tension applicators pulling machines calipers design
Tools for testing harnesses range from several-ton tension applicators (pulling machines) to simple calipers.Samantha Sanders

For the second test, there’s a large metal hoop fixed to a rectangular base, with a testing machine suspended above it. The harness is secured around the hoop and through the pulling apparatus, with the belay loop facing the sky. A series of two “pull, hold, release” sets follow, with a force that gradually increases to 10 kN. The harness is then checked for slippage above 20 mm. This test is the litmus test for belt slippage: It creates ideal conditions to cause movement in the waistbelt and to make sure your harness never comes undone, even in violent falls.

While not exactly real-world scenarios, these tests have two things going: 1) They allow the experiments to be easily reproduced. And 2) Your dynamic rope plus soft catch create less impact (i.e., less pulling) than what the dummy undergoes. In fact, 15 kN would destroy the human body.

Tom Fayle director of advanced research and development Arc’Teryx webbing rock climbing harness design testing
Tom Fayle, director of advanced research and development at Arc’Teryx, scopes a piece of webbing to assess the finer details of construction.Courtesy of Arc’teryx

Have a 225-pound friend stand on your waist. This is 1 kN. Now, have 14 other similarly sized friends pile on—that’s 15 kN. So next time you’re in the gym taking whippers, be thankful for that dummy taking the 3372.13 pounds of testing force for you. As Rick Vance, vice president of quality at Black Diamond, puts it, “The standards are set up to test to more rigorous demands than your harness should ever undergo in the real world”—where these forces can, for a climber weighing 132–200 pounds, range from 3.4–4.5 kN for a .5 fall-factor fall (a standard whipper) or 5.4–7 kN for a 1.5 fall-factor fall—or about the hardest catch you’ll hopefully never experience.

Finally, virtually all harness accidents are the result of user error, not a flaw with the harness. Your harness is designed to take more of a beating than you can give it. However, these tests are conducted on new harnesses, and a harness is only as good as its correct usage and condition. So educate yourself, wear and use your harness correctly, and remember to inspect it regularly.

Harness Care 101

The first step to assuring your harness is safe is you, so do a thorough inspection when you climb.


If wet, let your harness drip-dry before storing, and store away from temperature extremes, nibbling pests (mice!), chemical contaminants—battery acid, ammonia/cleaning products, or more exotic chemicals like aquarium pH decreaser—and sunlight, which bleaches and weakens nylon.


“A poorly fitting harness can be dangerous,” says Dan Middleton, technical officer at the British Mountaineering Council. “Check that you hang upright, ensure that it’s correctly adjusted, and that you won’t slip out in an inverted fall.”


A clean harness (wash per brand instructions) is a happy harness—the increased friction that dirt, grime, and grit create on moving surfaces (like the rope sliding through your tie-in points) abrades the nylon. Even metals can fall prey to humidity or particular conditions like highly saline environments. Particulates like salt aren’t always visible—give your harness a washdown if climbing near the sea.


The areas that tend to wear the fastest are the tie-in loops and belay loop—i.e., any load-bearing member that sees rope abrasion or heavy usage. If you’re noticing a fuzziness or pilling, or fraying or thinning, check other, less visible areas and make sure there’s nothing covering the area, like tape or a PAS.

Cuts and tears

Often stemming from improper storage (are there pointy things in your bag?), accidents, or abrupt loading (falling, especially on sharp rock), this appears about as you’d expect: material separating in places where it shouldn’t.

Hard-component damage

Rust is commonly seen on metals in saltwater environments, but can also be a sign of unmaintained gear or flaws in the metal coating. Though you can sand off surface oxidation, be aware of further damage it may be hiding. Also look for cracks or deformation.

Swelling and deformation

Contact with chemicals, heat, or repeated rough use can lead to changes in the soft fabrics. Harnesses can melt, act oddly in extreme cold (avoid temps of -80 F or below), and swell. (Visit Black Diamond’s Electric Harness Acid Test for a case study about a mysterious harness failure.)

Color change

Color change to the nylon is often indicative of damage, whether from UV radiation, chemicals, or old age. Standards require that structural threading (like the bartacks on your belay loop) are a different color than nearby webbing. Thus, if these threads or the materials are no longer their original color, your harness may have been contaminated and is in need of retirement. 

Samantha Sanders is a mechanical/materials engineer at a Seattle-based startup. Living for adventure, she climbs, bikes, skis, and runs, all while keeping an eye on the mechanics and design of her gear.