Accessory Cord for Climbing

The difference between alpine accessory cords comes down to diameter (thickness), material composition (nylon vs. high-modulus polyethylene/aramid), strength ratings, and stretch characteristics, which dictate what tasks they can safely perform.

Recomendation

21 feet of Mammut 7 mm Accessory Cord (7.0 Cord) or Sterling 7 mm Nylon Accessory Cord

• Strong enough to be used as an Anchor

  • 7mm is almost twice as strong of 6mm

  • 6mm isn't ideally strong enough for anchor use

• Multiple Rescue Uses

• Can be used for Prusik Hitch

  • Doesn't melt like Dyneema 

  • Not stiff like Sterling PowerCord (Technora) or BD Infinity Cord (Dynex) 

  • 7mm cord is good for ropes around 9-11mm

  • 7mm is a bit too big for 8.5mm apline climbing rope - 6mm Nylon or 6.8mm HollowBlock works better

  • 5mm is too weak for most safty applications 

Diameter & Strength

• 3-4 mm

  • Lightweight and handy for low-load tasks like gear ties, tent guy lines, makeshift clotheslines, and zipper pulls

  • Not strong enough for life-safety anchoring or body weight

• 5mm

  • Breaking Strength: 5.5 kN for Nylon Cord

  • Can be used for Prusik Hitch

  • NOT for use as anchors

• 6mm

  • Breaking Strength: 7.5 kN for Nylon Cord

  • Can be used for Prusik Hitch

  • Sometimes used for snow anchors where lower forces are expected

  • This is TOO Weak for rock climbing anchors 

• 7mm

  • Breaking Strength: 13 kN for Nylon Cord

    • At close to double the strength of 6mm, this is preferred for anchor use

  • Can be used for Prusik Hitch - but is a bit big

  • The standard size for general-purpose anchor building and multi-strand cordelettes

  • AMGA training often defaults to 7 mm nylon as a robust baseline for rock climbing anchors where impact forces are higher

Fall Factor

• Calculated as Fall Distance ÷ Rope Length Paid Out

• Ranges from 0 to 2

Forces by Fall Type

• Static Weight

  • 80 kg (176 lbs) person exerts about 0.784 kN of static force just by standing or hanging

• Top-Roping

  • Generates near-zero fall factors 

  • Roughly 1 kN of force

• Typical Lead Falls

  • Generate around 2-5 kN 

  • Fall factors usually between 0.2 and 0.7

• Factor 1 Falls

  • Lead climbing falls generate impact forces between 4 kN and 9 kN because the dynamic rope, harness, and belay device stretch and absorb a large portion of the kinetic energy

• Factor 2 Falls 

  • Worst-case scenario where a leader falls past the belay anchor with no protection clipped beyond belay anchor

  • Can push forces toward 12 kN to 20 kN

    • Exceeds safe human tolerance

    • Risks severe injury and gear failure

• OSHA Limits (Industrial/Rescue)

  • Caps maximum arresting forces to prevent severe physiological damageOccupational safety standards limit forces on a human

  • 4 kN (900 lbs) for body belts 

    • Can result in spine injury

  • 8 kN (1,800 lbs) for full-body harnesses 

    • High-impact deceleration can cause severe pressure loads on internal organs (viscera), whiplash effects, or head-down trauma

Cord Materials

“You can have it strong, light, and cheap. Pick two.”

Climbing cords are made from several types of synthetic fibers, each with different strengths, weaknesses, and ideal applications. Material selection affects a cord's weight, strength, elasticity, knot security, abrasion resistance, and ability to withstand heat generated by friction.

Understanding these differences is especially important when selecting cord for anchor building, prusiks, autoblocks, rappelling backups, and rescue systems.

Nylon (Polyamide, Perlon)

Nylon is the traditional material used in climbing ropes and cords. Its combination of strength, flexibility, elasticity, and affordability makes it a versatile choice for general climbing applications.

Characteristics

• Strong, flexible synthetic fiber with good elasticity (stretch)

• Absorbs energy through elongation, helping reduce peak forces in certain loading situations

• Generally offers good knotability and handling

Advantages

• Affordable and widely available

• Good knot security and handling characteristics

• Greater elasticity than most high-performance cord materials

• Generally performs well in friction hitches and other applications requiring knots

Disadvantages

• Absorbs water, which can increase weight and reduce strength, depending on the product and conditions

• Relatively low melting point (approximately 450°F / 232°C)

• Can lose strength through prolonged UV exposure and environmental wear

• May generate or sustain damaging heat under heavy friction

UHMWPE (Ultra-High-Molecular-Weight Polyethylene)

Common Brand Names: Dynex, Dyneema and Spectra

UHMWPE is an exceptionally strong, lightweight synthetic fiber. Its high strength-to-weight ratio makes it popular in lightweight climbing slings, runners, and specialty cords. However, its low friction and limited elasticity require additional care when tying knots or using it in friction-based systems.

Characteristics

• Extremely high strength relative to its weight

• Very low stretch (hyperstatic behavior)

• Highly resistant to moisture and many environmental conditions

Advantages

• Exceptional strength-to-weight ratio

• Very lightweight and compact

• Excellent resistance to moisture and UV exposure

• Does not absorb water

Disadvantages

• Very low melting point (approximately 300°F / 149°C)

• Extremely slippery surface, making knots more susceptible to slipping if improperly selected or tied

• Poor choice for many friction-hitch applications because it can slip and generate heat

• Virtually no stretch, providing little energy absorption

  • Questionable use as Anchor

Knot Considerations

• Follow the manufacturer's approved knot recommendations

• A Triple Fisherman's Knot may be specified for certain applications, but no knot should be assumed safe for every UHMWPE cord

  • Pay particular attention to knot dressing, tightening, and tail length

  • Leave adequate tails as specified by the manufacturer

    • For some applications, 2-3 inches (5-7.5 cm) may be recommended, but this is not a universal guarantee against slippage

Aramid Fibers

Common Brand Names: Kevlar and Technora

Aramid fibers are high-performance synthetic materials valued for their strength, heat resistance, and low stretch. They are commonly used in specialty climbing cords where resistance to friction-generated heat is important.

Characteristics

• High tensile strength and very low elasticity

• Excellent resistance to high temperatures compared with nylon and UHMWPE

• Good resistance to cutting and abrasion, depending on fiber construction

Advantages

• High heat resistance, with some aramid fibers capable of withstanding temperatures well above 800°F (427°C) before decomposition

• Excellent strength-to-weight ratio

• Very low stretch

• Good resistance to abrasion and cutting

Disadvantages

• Sensitive to repeated sharp bending, tight creasing, and localized stress

• Can experience strength loss from repeated flexing and fatigue

• Generally more expensive than nylon

• Low elasticity means limited energy absorption

  • Questionable use as Anchor

• Some aramid fibers have relatively poor UV resistance and can degrade with prolonged exposure

Hybrid / Composite Cords

Many modern specialty climbing cords combine two or more fiber types to take advantage of their individual strengths while minimizing their weaknesses.

A common construction pairs an aramid core with a nylon sheath in a kernmantle design.

Example: Technora (aramid) Core with Nylon Sheath

• Aramid Core: Provides high tensile strength, heat resistance, and low stretch

• Nylon Sheath: Provides a more manageable, grippy exterior that improves handling and friction-hitch performance

• Combined Performance: Balances the heat resistance and strength of aramid with the flexibility and knotability of nylon

Advantages

• Combines the desirable properties of different fiber types

• Nylon sheath generally provides better handling and friction characteristics than exposed UHMWPE or aramid fibers

• Can offer improved durability and versatility for prusiks, autoblocks, and other specialty applications

Disadvantages

• More expensive than conventional nylon cord

• Performance depends heavily on the specific core and sheath construction

  • 5.9 mm PowerCord as a Prusik is stiff and doesn't grab and predictably as softer cords

    • Poor choice for many friction-hitch applications

• The sheath can wear through, exposing the core and compromising the cord

• Still requires inspection for abrasion, glazing, core damage, and other signs of wear

Knot Considerations

• Many nylon-sheathed hybrid cords can be tied with a Double Fisherman's Knot when approved by the manufacturer

• Some manufacturers or applications may call for a Triple Fisherman's Knot

• Always follow the cord manufacturer's instructions for knot selection, compatibility, and minimum tail length

Cordelettes 

A cordelette is one of the most versatile pieces of climbing equipment. Primarily used to build multi-point anchors, accessory cord also has numerous applications in technical climbing and rescue systems, including extending anchors, constructing equalized systems, hauling, and creating friction hitches.

The best cord depends on the intended application. Traditional nylon cord offers good knot security and some elasticity, while high-strength Technora and HMPE constructions provide greater strength-to-weight ratios but generally have less stretch and require more attention to knot selection and handling.

Recommended Cordelettes

Mammut 7 mm Accessory Cord (7.0 Cord)

• Diameter & Material: 7 mm, 100% polyamide (nylon) kernmantle construction

• Strength: 13.5 kN (3,035 lbs) minimum breaking strength

• Weight: 30 g/m

• Why it excels: A dependable, traditional nylon cordelette that balances strength, durability, knot-holding security, and manageable stretch. Suitable for building multi-point anchors, extending anchors, and general climbing and rescue applications

• Key advantage: Easier to tie and handle than many smaller-diameter, high-modulus cords. Certified to EN 564 and UIAA standards

Sterling 5.9 mm PowerCord

• Diameter & Material: 5.9 mm with a braided Technora (aramid) core and nylon sheath

• Strength: 19.7 kN (4,429 lbs) minimum breaking strength

• Weight: 24.8 g/m

• Why it excels: Exceptional strength for its diameter and weight. An excellent choice for lightweight alpine cordelettes, compact anchors, and haul lines

• Key trade-off: Technora has very little stretch compared with nylon. The cord is relatively stiff and can be more difficult to knot and untie. Avoid shock loading and inspect carefully for damage from repeated knotting and handling

• NOT Appropriate for Prusik Hitches

  • Too Stiff

  • Too Slick

Sterling 7 mm Nylon Accessory Cord

• Diameter & Material: 7 mm kernmantle construction, 100% nylon

• Strength: Approximately 12.4 kN (2,787 lbs) minimum breaking strength

• Why it excels: A traditional, versatile cordelette with a good balance of knot-holding security, durability, and elasticity. A solid choice for multi-pitch trad anchors and general climbing applications

• Key advantage: Nylon construction provides more elasticity than Technora or HMPE cords, helping reduce peak forces during loading

BlueWater 5.5 mm Titan Cord

• Diameter & Material: 5.5 mm actual diameter (marketed as 5 mm under EN diameter conventions), HMPE/Dyneema and nylon construction

• Strength: 13.5 kN (3,035 lbs) tensile strength

• Weight: Approximately 18 g/m

• Why it excels: High strength-to-weight ratio, excellent abrasion and cut resistance, and minimal elongation. Useful for lightweight alpine applications, slinging horns, and specialized anchor configurations

• Key trade-off: The slick HMPE core requires careful knot selection. BlueWater recommends a triple fisherman's knot when tying this cord into loops. Its low stretch also makes it less forgiving of shock loading

• NOT Appropriate for Prusik Hitches

  • Low Melting Point - can glaze, melt, or fail to grip properly 

  • Too Stiff of Prusik use

Prusik Hitches

A Prusik hitch typically "fails" either by slipping along the main rope or breaking at varying kN (kilonewton) thresholds depending on whether you mean slipping (grip failure) or cord breakage (structural failure):

• Slipping Failure (When the Hitch Starts to Slide)

  • First Slip / Slipped Grip

    • A standard 6mm accessory cord Prusik tied on an 8-10mm rope will often begin to slip or creep under loads around 2 kN to 3 kN (depending on the number of coils, such as 3-on-2 vs 3-on-3 wraps)

    • Per Prusik, Auto Blocks, and Klemheist Break Tests by HowNOT2

    • 4MM PARACORD on 10.5mm Dynamic Rope:

      • Prusik broke at 3.74kN

      • Klemheist broke at 3.34kN

      • Auto Block 3 wraps slips at 1.34kN

      • Auto Block 4 wraps slips at 5.32kN

      • Paracord doubled twice broke at 8.90kN

      • Paracord in a loop broke at 4.06kN

    • 5MM ACCESSORY CORD on 10.5mm Dynamic Rope:

      • Prusik broke at 8.16kN 

      • Prusik broke at 5.36kN

      • Klemheist slips at 3.3kN  

      • Auto Block: 3 wraps slips at 0.36kN 

      • Auto Block: 4 wraps slips at 3.62kN 

    • 7MM ACCESSORY CORD on 10.5mm Dynamic Rope:

      • Prusik broke at 7.9kN 

      • Prusik slips at 5.18kN

      • Klemheist slips at 3.3kN and tangles up with rope at 11.62kN

      • Auto Block: 4 wraps slips at 0.8kN 

    • old HOLLOW BLOCK on 10.5mm Dynamic Rope:

      • Prusik broke at 5.84kN (note: old HollowBlock was used)

      • Auto Block: 3 wraps slips at 0.42kN 

      • Auto Block: 4 wraps slips at 1.38kN 

  • Higher Load Slips

    • In some rescue testing configurations (like a 4-on-2 PMI 6mm Prusik on an 8mm rope), initial slips occur around 7.0 to 7.3 kN, eventually peaking near 9 to 10 kN before the cord fails inside the hitch

  • Self-Limiting Behavior

    • In climbing scenarios (like a cow-tail sling), a Prusik will intentionally slip under high impact loads, which helps absorb energy and cap the force transmitted to the climber well below dangerous thresholds

• Breaking / Structural Failure (When the Cord Snaps or Glazes)

  • Accessory Cord Tensile Strength

    • Standard 6mm to 7mm accessory cords typically have a free-length Minimum Breaking Strength (MBS) in the 7 kN to 10 kN range

    • Tied into a loop and loaded over a small radius, the knot configuration reduces the overall system strength

  • Melt-Through / Glazing

    • If a Prusik slides too far or too fast under a heavy load, the extreme friction generates intense heat, causing the sheath of the accessory cord to glaze, melt, or burn through long before reaching its static breaking point

    • HMPE/Dyneema is MORE susceptible to melting

    • Aramid is LESS susceptible to melting

  • Full Breakage

    • Studies on traditional Prusiks (such as 7mm cord on 11mm static line) show average breaking strengths around 12.36 kN

    • Heavy-duty configurations can range higher depending on cord material and diameter

Nylon Accessory Cord

• Prusik cord should generally be about 60% to 80% than the diameter of the main rope

  • Roughly 2mm to 3mm smaller than main rope

  • Minimum 5.5-6mm

  • Max 7mm

• Soft and Supple

  • Squeeze a bite of cord and the eye should just about disappear

• Regular cord from big retail stores won't work

  • Go to REI or climbing shop

• Breaking Strength

  • 5mm: 5.5 kN 

  • 6mm: 7.5 kN 

  • 7mm: 13 kN 

• Slippage Threshold

  • Generally slips rather than breaks under high or excessive loads

    • Heavily influenced by main knot used, rope's diameter, sheath treatment and whether rope is wet, dry, icy or slippery

  • 4mm or 5mm accessory cord or fewer wraps of larger cord will slip at lower forces 

    • Starting around 1.3 kN to 3.0 kN

  • 7.5mm on 11mm Rope slips at higher forces

    • 3-wrap Prusik often experiences its initial point of major slippage around 5.5 kN to 8.7 kN

• Selecting a Size

  • 5 mm

    • Can provide aggressive gripping

    • Has less material and generally less breaking-strength margin

    • Often NOT recommended

  • 6 mm

    • A good balance of grip, strength, and handling

    • Commonly recommended for Prusiks on modern climbing ropes

  • 7 mm

    • Offers greater cord strength in many constructions

    • Strong enough to be used as an anchor or other rescue uses

    • May require additional wraps or a different host-rope combination to grip reliably

• Lengths needed

  • 5mm to 6mm nylon or aramid cord joined with a double fisherman's bend

    • Abseil / Rappel Backup (Third Hand)

      • 30-35cm Loop (~1.2 meters / 4 feet of cord) 

    • Ascending or General Progress Capture 

      • 40-50cm Loop (~1.5 meters / 5 feet of cord) 

    • Foot Loops or Special Rigging 

      • 1-2 meters / 3-6 feet of cord

  • 7mm nylon for anchor and rescue use

    • Quad Anchor

      • 14 feet of 7mm cord makes a loop close to 190cm

      • ~17 feet of 7mm cord is needed for a 240m loop

    • Masterpoint

      • 21 feet of 7mm cord makes around a 300cm loop

    • Self Rescue

      • 20+ feet of 6-7mm cord

• Examples:

  • Mammut Pro Cord (6 mm)

    • Diameter & Material: 6 mm kernmantle construction, 100% nylon.

    • Strength: 7.5 kN (1,686 lbs) minimum breaking strength.

    • Weight: 22 g/m.

  • Sterling 6 mm Nylon Accessory Cord

    • Diameter & Material: 6 mm kernmantle construction with a 100% nylon core and sheath.

    • Strength: 8.2 kN (1,843 lbs) minimum breaking strength (MBS), according to Sterling's published specifications.

    • Weight: Approximately 23 g/m.

  • Mammut 7 mm Accessory Cord (7.0 Cord)

    • Diameter & Material: 7 mm, 100% polyamide (nylon) kernmantle construction

    • Strength: 13.5 kN (3,035 lbs) minimum breaking strength

    • Weight: 30 g/m

  • Sterling 7 mm Nylon Accessory Cord

    • Diameter & Material: 7 mm kernmantle construction, 100% nylon

    • Strength: Approximately 12.4 kN (2,787 lbs) minimum breaking strength

• NOT Appropriate for Prusik Hitches:

  • BlueWater 5.5 mm Titan Cord

    • HMPE/Dyneema and nylon construction

    • NOT ideal for Prusik Hitch

    • Low Melting/Heat Resistance Issues: Dyneema/HMPE has a low melting point. If used in a traditional binding Prusik where heavy friction builds up (such as rappelling with a Prusik backup under high speed or load), the cord can glaze, melt, or fail to grip properly compared to aramid/Kevlar-blend cord (like a Bluewater VT Prusik or Sterling Hollow Block).

    • Stiffness and Knot-Holding: Titan cord is quite stiff and slick compared to soft nylon or aramid/tech cords. Traditional knots like a classic three- or four-wrap Prusik can be difficult to set, tend to slip or fail to bite reliably on standard single ropes, or conversely lock up too rigidly depending on the host rope diameter.

  • Sterling 5.9 mm PowerCord

    • Diameter & Material: 5.9 mm with a braided Technora core and nylon sheath

      • Technora Heat Resistance: Withstands continuous temperatures up to 200°C (392°F) and has a thermal degradation threshold above 500°C (932°F)

    • NOT ideal for Prusik Hitch

    • Stiffness and Memory: It features a high-tenacity Technora core and a nylon sheath, making it very stiff and static with a noticeable "memory," which prevents it from being supple enough to easily bite and grip a main rope

    • Slickness: The lack of flexibility and the smooth high-strength core/sheath interaction mean it struggles to set and release smoothly as a friction hitch

Sewn Prusik Cord 

• 7mm max size for most climbing

• 8mm used with 11mm static ropes which are in turn used for rescue

• HollowBlock2 (Sterling Rope):

  • 6.8mm square shaped hollow braid

    • Aramid fiber

    • For use on 7 mm or larger rope

  • Breaking Strength: 14kN 

  • Sizes

    • 13.5-inch (34 cm) loop 

      • Traditional prusik knot 

      • Standard wrap-around-the-leg autoblock (rappelling backup / third hand)

    • 19-inch (48 cm) loop 

      • French Prusik

      • Klemheist knot

      • More complex multi-wrap friction hitches for rescue use

• BlueWater VT Prusik

  • Structured cord with an aramid sheath

  • Kernmantle-style construction with an aramid sheath over a core (often sewn eyes/loops)

    • Longer working life compared to the sheathless HollowBlock

  • Breaking Strength:

    • BlueWater 8mm VT Prusik Basket (looped / both eyes clipped) 29.5 kN  

    • BlueWater 7mm VT Prusik Basket (looped / both eyes clipped) 22.6 kN

  • Tied as a Valdotain Tresse (VT) or asymmetric/wrap-and-braid style hitch

    • Takes slightly longer to dial in and tie properly than an French Prusik (autoblock)

  • Smoother release and better hand feel during operation than HollowBlock

• Beal Jammy

  • 5.5mm diameter

    • Polyamide (nylon) sheath

    • Aramid core

  • Breaking Strength: 22 kN

  • 35cm length - traditional Prussic

  • 50 and 60cm - French Prusik or Klemheist

  • It is important that your knot is well dressed, or your Prusik will slide and bunch up

Anchor Cord Loops

7mm Alpine Cordelette 

• • Multiple uses

    • Recommend 21 feet of 7mm cord

    • Note: a Double Fisherman's Knot for 7mm climbing accessory cord will consume roughly 35-40 cm of the cord's overall length

    • Quad Anchor

      • 14 feet of 7mm cord makes a loop close to 190cm

      • ~17 feet of 7mm cord is needed for a 240m loop

    • Masterpoint

      • 21 feet of 7mm cord makes around a 300cm loop

    • Self Rescue

      • 20+ feet of 6-7mm cord

  • Breaking Strength

    • 5mm cord: ~5.1 kN

    • 6 mm cord: ~7.5 kN 

    • 7 mm cord: ~13 kN  

      • At almost twice the breaking strength, 7mm is preferred over 6mm for anchor use

      • 5mm is NOT appropriate for anchor use

      • 6mm is NOT recommended for anchor use on Rock (but could be considered for glacier use)

  • Weight

    • Around 110g for 21 feet of 5mm cord

    • Around 140g for 21 feet of 6mm cord

    • Around 200 g for 21 feet of 7mm cord

  • Best Examples

    • 7mm Sterling Accessory Cord

    • 7mm Mammut Cord 

BD Infinity Cord - 240cm

• • 4.5 mm Continuous loop of Dynex (Dyneema) filament core inside a Dynex/nylon blend sheath

  • Breaking strength of 22 kN+

  • 62 g 

  • Easy to untie knots

  • NOT great for Prusik Hitch

    • Too Slippery: The continuously woven Dynex/nylon sheath and core construction is specifically designed to be stiff, malleable, and low-friction so that knots never weld shut under a heavy load. Because a friction hitch relies on the cord biting and gripping the rope, a slippery material like the Infinity Cord may fail to grab properly or can slip uncontrollably

    • Diameter and Construction: At about 4.5 mm thick, it is much thinner and stiffer than standard accessory cord or sewn prusik loops (like a Beal Jammy or traditional 6mm–7mm cord/hollow block), which are specifically engineered with aramid-nylon blends to catch reliably

Metolius Open Loop Sling - 240cm

• • 11mm wide Dyneema and Nylon fibers

  • Very easy to untie knots after they have been weighted

  • 22 kN rating

  • 93 g

  • Note: formerly known as Monster Sling

  • Quad Configuration

    • Doubled up and tied with knots on two separate bolts or pieces, a standard quad distributes the load across multiple strands, yielding a total system strength around 40 kN (before tying knots)

  • Knot Strength Reduction

    • Knots reduce the strength of individual Dyneema strands by roughly 40% to 50%

    • Double-redundancy of the quad setup compensates for this loss, basically bringing the breaking point back down to around 22kN

  • Shock Loading Risk

    • Unlike nylon, Dyneema has very low stretch and minimal energy absorption

    • A severe fall directly onto a rigid Dyneema anchor can generate high shock loads

    • There is a valid concern that falling from above the anchor can cause a significant shock to Dyneema

  • NOT appropriate for Prusik Hitch

    • Material and Friction: Most Metolius Open Loop Sling options (such as their 11mm or 13mm thin Dyneema/nylon blend Monster slings) or pure nylon open slings are flat webbing rather than round cord. Flat webbing does not bite or wrap smoothly around a climbing rope to form a reliable, self-tightening and self-releasing Prusik hitch

    • Low Heat/Friction Resistance: Dyneema and UHMWPE blends have a very low melting point and high slipperiness. If a flat Dyneema sling is used as a friction hitch and slips under load, it can glaze, melt, or fail catastrophically from frictional heat

    • Improper Cord Diameter Ratio: A proper Prusik requires a friction-hitch cord (typically accessory cord around 5mm to 7mm) that is noticeably smaller in diameter than the main rope (usually 9mm to 11mm) to ensure it grips and grabs properly. Flat runners or thick open loop slings do not have the right diameter-to-stiffness ratio

    • Wear and Tear: Using flat slings as a Prusik causes rapid, severe surface abrasion and structural damage to the sling long before normal wear and tear would occur