A fiber name is not a specification.

Fibers separate by behavior, not by rank

Product listings tend to compress a fiber into one adjective: nylon is “stretchy,” polyester is “tough,” polypropylene is “cheap,” HMPE is “strong.” Those shorthands are not wrong so much as unfinished. A fiber is better understood as a set of behaviors that trade against one another.

• Water: does the fiber absorb it, and does absorbing it change the fiber?
• Density: does the fiber float or sink?
• Heat: at what temperature do properties start to fall off, and what happens at the extreme?
• Sunlight: how quickly does ultraviolet exposure erode the material?
• Stretch and time: how much does it move under load, does the movement come back, and does it keep moving?
• Wear, hand, and cost: how it abrades, how it feels and knots, and what it costs to replace.

No common fiber wins every column, which is why a “best rope material” question rarely has an answer. Cortland International puts it plainly in its rope user manual: “the selection of a rope always involves compromises based on the type of service.”

The four fibers most comparisons come down to

Qualitative comparison. Scroll sideways on a narrow screen.

Aramids, liquid crystal polymer, and natural fibers matter too, and they are covered further down. But most everyday and light commercial decisions land somewhere inside those four.

Water changes the comparison

This is the clearest real difference between the two most common fibers. Nylon takes on water; polyester essentially does not. In Cortland’s published fiber table, nylon is listed at 2–6 percent water absorption while polyester, polypropylene, and HMPE are listed as none. The manual states directly that polyamides “will absorb water and lose strength when wet,” and that polyesters “do not lose strength in water.”

That is a relative statement, not a failure warning. Wet nylon rope is used constantly and appropriately. It does mean that a nylon line’s dry rating and its wet behavior are not the same claim, and that a comparison made on a dry bench does not automatically hold on a wet dock.

One distinction is worth holding onto: this effect is largely reversible. Sterling Rope’s technical manual describes nylon as hydrophilic, says “the overall strength and stretch can be greatly affected by moisture in the fiber,” and then adds that “nylon’s original strength and elongation returns when the rope dries.” Wet is a temporary condition. Ultraviolet exposure, heat damage, and abrasion are not—they are cumulative and permanent. Do not treat those categories as interchangeable kinds of “wear.”

Floating is a density question

A fiber floats in water when its specific gravity is below 1.0. Cortland’s table lists polypropylene at 0.91 and HMPE at 0.97—both below water—while nylon is 1.14 and polyester is 1.38, both of which sink. That is why a throw line or a line you need to see on the surface is usually polypropylene or an HMPE blend.

Flotation is a property of the fiber, not a promise about the finished rope: coatings, cores, blends, and absorbed water and grit all move the answer. And flotation is a poor reason to select a loaded line, which is why the marine application page lists “choosing polypropylene only because it floats” as something to stop doing.

Melting point is usually the wrong number

Fiber comparison charts love melting points, but a rope almost never fails by melting. It loses strength long before that, and it gets there through friction—a line surging around a bollard, a fast descent, a winch drum, a rope sawing against another rope. Cortland’s manual notes that “virtually all synthetic fibers can be melted or charred due to exposure to elevated temperatures,” and that heat damage shows up as glazed, fused, or brittle fiber.

The more useful published figure is a working or critical temperature. Cortland defines its critical temperature as “the temperature beyond which mechanical properties of the fiber are reduced,” and the values reorder the comparison sharply: it lists 65 °C (150 °F) for both polypropylene and HMPE, 162 °C for polyamide, and 177 °C for polyester. The same manual instructs that polypropylene, HDPE, and HMPE ropes “must not be used in loading conditions with temperatures greater than 150°F (65°C).”

That gap is the practical lesson. HMPE is the strongest fiber in the group and one of the least heat-tolerant. A number that sounds like an oven temperature is in fact reachable on a dark rope on a hot deck, or in seconds at a friction point.

Aramids sit at the other end and behave differently in kind. Teijin describes Twaron as having a “decomposition temperature above 500 °C” and says it “chars rather than melts.” DuPont’s technical guide for Kevlar aramid fiber states the same thing about that fiber: it does not melt, it decomposes, at roughly 427–482 °C in air. High heat tolerance does not make aramid the general answer, as the next sections explain.

Treat all of these as published fiber values from the companies that sell the fiber. A finished rope’s usable service temperature belongs to the product and its data sheet, not to the fiber family.

Sunlight is a slow, invisible load

Ultraviolet light degrades polymers. That is why rope storage guidance is consistent across the industry—Cortland’s manual says rope should be stored “out of direct sunlight and/or any source of ultraviolet light”—and why an outdoor line has a service life that has nothing to do with how many times it has been loaded.

Beyond that, be careful. Published UV rankings disagree with one another, and the figures circulating online—a given percentage of strength lost in a given number of months—depend on latitude, season, cumulative exposure, rope color, coatings, additive packages, and the test method used. We are not repeating those numbers, because a UV figure that is not tied to a stated test and exposure is not transferable to your rope.

What is safe to say is directional. Polyester is generally rated at or near the top of common fibers for sunlight resistance. Polypropylene is routinely sold with UV stabilizers precisely because unstabilized polyolefin does poorly outdoors, so “UV stabilized” on a polypropylene label is addressing a known weakness rather than adding a bonus. And aramid is UV-sensitive: DuPont’s Kevlar technical guide states that unprotected yarn discolors with prolonged exposure and that extended UV exposure “can also cause loss of mechanical properties,” which is part of why aramid usually appears in rope as a core underneath a cover.

There is also a variable most comparisons omit entirely: diameter. DSM Dyneema’s bulletin on outdoor use explains that “ultraviolet radiation only penetrates to shallow depths, causing small diameter ropes to be affected much more than large diameter ropes.” Its own ten-year outdoor exposure testing ran on samples from 0.5 mm to 8 mm and showed the thinner ones losing retained strength markedly faster. A UV rating attached to a fiber, with no diameter attached to it, is telling you less than it looks like it is—and the same bulletin advises “protective measures such as coatings or non-load bearing jackets” for long sun exposure.

Practically, UV damage arrives from the outside in. A line that has gone chalky, faded, or fuzzy has an exposure history you cannot measure by looking at it—and Cortland’s manual is blunt that “a visual inspection can only provide a subjective estimate on retained strength.”

Stretch that returns, and stretch that does not

At least three different things get sold as “stretch,” and mixing them up produces bad predictions.

• Elastic elongation is the stretch that comes back when the load comes off. This is the stretch nylon is chosen for.
• Constructional elongation is the one-time bedding-in as a new rope’s fibers and strands settle. Cortland calls it “almost irreversible” and notes that published load-versus-elongation curves “are approximations and do not include constructional stretch.”
• Creep is permanent elongation that keeps accumulating under sustained load. It does not come back.

Creep is where the polyolefins are exposed. Cortland states that “creep is non-recoverable plastic elongation” and that “polyolefins like HDPE, PP and HMPE are more heavily affected by creep compared to other fibers, especially at elevated temperatures.” If a line will hang under steady tension for months—a permanent guy, a standing stay, a long-term mooring—that is exactly the loading creep punishes, and it is a real argument against polypropylene and against the wrong grade of HMPE.

Before that hardens into a fear of HMPE, note the balancing point from the fiber maker itself. Avient’s technical bulletin on Dyneema creep resistance says that “most ropes made with UHMWPE fibers are not subjected to constant loads or are used at low average temperatures,” and that “for those, the creep property is not relevant.” Creep is a loading-condition problem, not a property that makes the fiber generally unsuitable.

When it does apply, the grade is the point. The same bulletin states that “the level of irreversible elongation of UHMWPE fibers is dependent upon the fiber grade, time, tension and temperature,” and publishes an illustrative comparison for a 1,000 kN rope held at 200 kN and 20 °C: a creep rate of 2.6 percent per year for Dyneema SK75, 0.9 percent for SK78, and 0.0 percent for the purpose-built DM20 grade. Avient footnotes those values as “only indicative.”

Read that footnote as seriously as the table. Two ropes can both be honestly advertised as Dyneema and behave completely differently over a year of standing load, and even the manufacturer will not treat its own published figures as design values. That is the strongest argument in this article for reading the specific product’s data sheet rather than the fiber name.

For how elongation, load, and strength ratings relate to each other as claims, see breaking strength is not a working load.

Aramids, LCP, and natural fiber

Aramids (Kevlar, Twaron, Technora) are high-modulus fibers with very low stretch and excellent heat tolerance. Cortland’s manual characterizes them as “specialized for elevated temperature applications” with “great creep resistance,” while noting they are heavier and less abrasion resistant than HMPE. Combined with UV sensitivity, that is why aramid tends to appear as a protected core rather than as a bare rope.

Aramid also has a failure mode with no equivalent among the common fibers, and it is worth knowing the name. The American Bureau of Shipping defines axial compression fatigue as “a failure mode for fiber rope such as aramid under low tension or compression”—damage that accumulates when the rope goes slack rather than when it is loaded. ABS records that “early experience with aramid rope in mooring applications has not been favorable” because of it, that keeping the rope in tension did not solve the problem since “some fibers at the splice can still be subjected to axial compression fatigue even though the whole rope is in tension,” and that this “caused the industry to turn away from aramid rope for an extended period.” It is a good reminder that a fiber’s weakness is not always visible in a properties table.

Liquid crystal polymer (Vectran) is described in the same manual as having “the best creep resistance of any fiber,” which is why it turns up where dimensional stability under standing load matters more than cost. PBO (Zylon) has the highest strength of the group but, per the same source, “degrades rapidly in both water and sunlight”—a useful reminder that headline tenacity and field durability are unrelated questions.

Natural fibers—manila, sisal, hemp, cotton—absorb water, are subject to rot and biological attack, and vary with the plant, the growing season, and the batch in a way synthetics do not. They remain a reasonable choice for grip, hand, appearance, traditional rigging, and jobs where the rope is frankly a consumable. We are not publishing comparative strength figures for them here, because we could not find a current, neutral, primary source we were willing to stand behind.

What the fiber name still does not tell you

Two ropes labeled with the same fiber can differ enough that the label stops being predictive. Cortland states it directly: “not all synthetic fiber ropes are designed and produced the same; raw material choice, quality, construction, and coatings vary by manufacturer.”

Within one fiber name, all of the following still vary:

• Fiber grade — the SK75-versus-SK78 creep difference above is the clearest example, but grade tiers exist across most high-performance fibers.
• Yarn quality and blend — including blends that carry a recognizable fiber name while behaving like a compromise.
• Construction, twist, and braid level — covered in twisted, braided, kernmantle, and double braid.
• Coatings and finishes — which change surface friction, abrasion resistance, and how the rope holds a knot.
• What the published number means — minimum breaking strength, average break, and working load limit are different claims about the same rope.

The most direct statement of this comes from a neutral source rather than a rope maker. The American Bureau of Shipping, writing design guidance for offshore mooring, states that “comparison of alternative fiber ropes in terms of their mechanical properties alone is not sufficient for design; the relative merit of each fiber rope can only be assessed through comparison of… performance obtained from a detailed… analysis.” And of its own published fiber comparison table, ABS says simply: “note the values in this table are indicative only and should not be used for design.”

A classification society declining to let its own table be used for design is about as clear a signal as this subject offers. Every comparison table on this page, including ours, is a way of narrowing a question—not of answering it.

So the honest sequence is: use the fiber to eliminate obviously wrong candidates, then use the specific product’s data sheet, its stated test conditions, and its instructions to choose among what is left. Where the consequence of failure is serious, that choice belongs with a qualified person and the controlling standard rather than with a comparison table.

Primary and technical starting sources

• American Bureau of Shipping, Guidance Notes on the Application of Fiber Rope for Offshore Mooring (2011)Classification society guidance · copy hosted by BSEE (US Department of the Interior)
• Cordage Institute rope terminologyTrade association reference
• Cordage Institute publications catalogStandards and guideline catalog
• Cortland International, Synthetic Fiber Rope User’s Manual (2025)Manufacturer technical manual
• Avient, CIS YA104: creep resistance of Dyneema fiber (2024)Manufacturer technical bulletin
• DSM Dyneema, CIS YA103: outdoor use of ropes made with UHMWPE fiber (2016)Manufacturer technical bulletin
• Marlow Ropes, understanding elongation and creep in HMPE ropesManufacturer technical note
• Sterling Rope, Guide to Rope Engineering, Design, and Use, Volume 1Manufacturer technical manual · undated, mirrored copy
• Teijin Aramid, Twaron product technical informationManufacturer product data

Statements attributed to DuPont in this article come from its published Kevlar Aramid Fiber Technical Guide. We have not linked it because the manufacturer’s hosted copy currently redirects; check the current publisher’s site for the live edition.

Sources checked August 3, 2026. Manufacturer literature describes that manufacturer’s products. Check the current official text and the exact product documentation before relying on a consequential claim.