Rope Strength

When you are choosing a rope, there are a few things you need to consider—tensile strength, breaking strength, and working load.

But what do those mean? And why does it matter?

In this article, we will break it all down for you.

So, let’s start!

Tensile Strength of a Rope

Now let’s clear up a big myth: tensile strength.

This is the maximum load a brand new rope can withstand before it breaks in a controlled lab environment.

This is what rope manufacturers test in the lab under ASTM test method D-6268.

How do they do it?

The rope is stretched around two large capstans and tension is increased gradually until the rope breaks. They average out several tests to find the rope’s tensile strength.

Some manufacturers mention the minimum tensile strength instead of the tensile strength.

It is calculated by reducing the average strength by 20% to account for factors like age and use.

Working Load Limit of a Rope

As you can see, the tensile strength gives you the rope’s maximum load under new conditions. But ropes don’t stay brand new for long, right?

That’s where the working load limit (WLL) comes in. It is the safer, real world limit.

It’s usually 15-25% of the rope’s tensile strength. This is a safety margin for daily wear, knots, and environmental conditions.

For example, if your rope has a tensile strength of 3,500 lbs, the working load limit would be around 700 lbs.

Sometimes, the reduction factor can be as low as 10% for safety-critical applications, like life-saving equipment, while some low-stress environments may permit a WLL closer to 30% of tensile strength.

Check the manufacturer’s label on their packaging for accurate data.

And here’s an important thing to note: knots weaken ropes.

Some knots like the Figure 8 reduce rope strength by 35%, others can reduce strength by up to 50%.

Tensile Strength vs Working Load Limit

Let’s break down the difference between tensile strength and working load limit.

Factor	Tensile Strength	Working Load limit
Definition	The maximum load a rope can withstand before it breaks in controlled conditions.	The safe maximum load a rope can carry in normal use, taking into account wear and environmental conditions.
Calculation	Tested in the lab by applying increasing tension until the rope breaks.	Typically 15-25% of the tensile strength.
Strength Factors	Measured without knots, friction or environmental stress.	Accounts for real world factors like knots, bends, abrasion and weather.
Safety Margins	No safety margin.	Has a built in safety margin, usually 5 times less than the tensile strength.
Real World Examples	Used to test the maximum strength of new, unused ropes.	Used in normal use where safety and consistency is critical.
Impact of knots	Not included as tensile strength is for an unknotted rope.	Tying a knot can reduce the WLL by up to 50%.
Example for Nylon (½ inch)	3,537 lbs (maximum load under lab conditions).	707-884 lbs (safe load for regular use).

Rope Testing and Care

When you start using ropes it tends to loose it strength as it goes to several abrasion cuts and environmental conditions.

Rope care is key to retaining your ropes strength and extending their life.

Here’s how to do it:

• Avoid abrasion: Use chafing gear to protect the rope from hard surfaces.
• Watch for kinks: These will weaken the rope over time.
• Store properly: Keep synthetic ropes out of direct sunlight, and natural fibers dry to prevent rot.
• Avoid sharp bends: Any sharp angle will weaken the rope so pad it or avoid it if possible.
• Flip the ends: Use both ends of the rope to distribute wear evenly.

Natural Ropes and Their Strength

While synthetic ropes rule many industries, natural ropes are still used for their strength and traditional feel.

But they don’t perform well in moisture heavy environments and prone to rot—except for manila rope which is an exception.

Let’s take a look at these ropes.

Cotton Rope

Let’s start with cotton, the softest and most eco-friendly rope.

Cotton ropes are gentle on the hands and good for light work. They absorb water easily which makes them not ideal for wet environments, but great for indoor projects like arts and crafts, macrame, pet toys.

Strength: Low tensile strength, not for heavy loads

Pros: Soft, eco-friendly, biodegradable

Cons: Absorbs water, fades in sunlight

Common Use: Art and crafts and macrame

For a bit more durability, you can go for jute and sisal ropes.

Jute and Sisal Rope

Jute comes from plant fibers and is good for arts and crafts. Sisal is a bit stronger and more durable, ideal for indoor projects.

Both are natural and biodegradable.

Strength: Moderate tensile strength (Sisal)

Pros: UV resistant, biodegradable, strong grip

Cons: Stiff (sisal), can wear out quickly (jute)

Common Use: Craft projects, gardening, agriculture

Next is the classic manila rope, known for its traditional look and outdoor durability.

Manila Rope

Manila is the strongman of natural ropes.

It’s tough and reliable but has limits in wet conditions where it absorbs water and rots over time.

Still, it’s the rope you think of for classic tug-of-war or old-school outdoor setups.

Strength: High breaking strength for a natural fiber but weakens when wet

Pros: Good grip, durable in dry conditions, hold knots well

Cons: Absorbs water, rots, not safe for pets

Common Use: Landscaping, tug-of-war, gym climbing rope

Here’s a quick snapshot of the properties of natural ropes:

Properties	Sisal	Manila	Cotton
Abrasion Resistance	Moderately High	Moderately High	Low
Resistance to Acids	Poor	Poor	Poor
Resistance to Alkalis	Fair	Fair	Fair
UV Resistance	High	High	Hight
Resistance to Rot and Mildew	Low	Low	Extremely Low
Shock Loading	Poor	Poor	Very Poor
Strength	Low	Low	Low
Durability	Moderately High	Moderately High	Low
Stretch	Extremely low	Extremely low	Low
In water	Dips	Dips	Dips
Storage	Dry	Dry	Dry

Synthetic Ropes and Their Strength

Synthetic ropes are made from man made materials and are strong and durable.

What really sets them apart is their performance in wet conditions. These ropes don’t absorb much water and are rot resistant.

You’ll see them in high-friction scenarios like winching, off-roading, sailing or tying down cargo.

Let’s break down the main types of synthetic ropes below.

Polypropylene Rope

Polypropylene is a lightweight, cheap synthetic rope that people first think of when they think of rope.

It’s resistant to moisture so can be stored indefinitely in wet environments. Not as strong as other synthetics, but it’s good for general purpose use.

Strength: Moderate strength

Pros: Floats, UV resistant, rot proof, cheap

Cons: Less durable than Nylon or Polyester

Common Use: Swimming lanes, cable pulling, marine work

Now, we move on to polyester rope which is way more durable.

Polyester Rope

Polyester is the all around workhorse. It outlasts other synthetic fibers including Nylon and Polypropylene.

It’s stronger than polypropylene and resistant to UV rays, chemicals, and water.

Good choice for marine applications and heavy duty outdoor tasks.

Strength: High tensile strength, retains strength when wet

Pros: UV resistant, rot proof, abrasion resistant

Cons: Stiffer than nylon, sinks in water

Common Use: Anchors, tie downs, sailing, flagpoles

Nylon Rope

Nylon is a beast when it comes to strength and flexibility. It’s great for absorbing shock loads, so it’s great for towing, fall protection, and pulleys.

But it does absorb water which weakens its strength over time.

Strength: High tensile strength, great elasticity

Pros: Strong, UV resistant, abrasion resistant, stretches up to 20%

Cons: Absorbs water, weakens when wet

Common Use: Towing, fall protection, pulleys, anchor lines

HMPE Rope (Dyneema)

This rope takes the prize for strength-to-weight ratio. HMPE ropes are at least 8 times stronger than steel by weight.

They’re lightweight, UV resistant and good for heavy duty use like industrial winching or marine work.

But, they don’t absorb shock loads well.

Strength: Incredibly high tensile strength, lightweight but can hold heavy loads

Pros: Strong, lightweight, UV resistant, abrasion resistant

Cons: Low shock absorption, static, hard to tie knots

Common Use: Industrial winching, towing, cranes, water sports

Here’s a quick snapshot of the properties of synthetic ropes:

Properties	Nylon	Polyester	Polypropylene	Polyethylene
Abrasion Resistance	High	High	Moderately High	Moderately High
Resistance to Acids	Fair	Good	High	High
Resistance to Alkalis	Very good	Fair	High	High
UV Resistance	High	Extremely High	Moderately High	Low
Resistance to Rot and Mildew	High	Extremely High	Extremely High	Extremely High
Shock Loading	Excellent	High	High	Fair
Strength	High	High	Moderately High	Extremely High
Durability	High	High	High	Extremely high
Stretch	High	Low	Low	Extremely Low
In water	Dips	Dips	Floats	Floats
Storage	Wet or Dry	Wet or Dry	Wet or Dry	Wet or Dry