Editor: Otto Tromm | Test date: 4 Jun
Old rope gets thrown away — that is the assumption. But what if a length of polypropylene rope that is 10 years old and poorly stored still performs remarkably well in a breaking strength test? This result warrants a closer look, as it runs counter to what most professionals would expect.
We also have 2 reference tests for comparison: one from another 10-year-old rope and one from a 7-year-old rope.
The earlier test on the 10-year-old rope can be found here: https://prorope.eu/blogs/news/8-mm-polypropylene-10-year-old-rope-breaking-strength-test
The test on 7-year-old polypropylene rope can be found here: https://prorope.eu/blogs/news/4-mm-polypropylene-orange-rope-7-5-years-old-breaking-strength-test
The average breaking strength of this 10-year-old, poorly stored 8mm polypropylene rope is 7.99 kN (814 kg), measured across 5 tests with a highest value of 8.30 kN and a lowest of 7.66 kN.
Storage conditions do have a measurable effect — nearly 200 kg less compared to a better-stored specimen of the same rope.
The rope is therefore still strong, but no longer meets the ISO standard.
What is 8mm polypropylene rope?
Polypropylene (PP) is a synthetic fibre with a low density: the rope floats on water. The construction of this specific rope is 3-strand twisted, the classic twisted construction in which three strands are wound around each other.
This is the most traditional construction for PP rope and the easiest to splice.
Polypropylene has the lowest UV resistance of all common synthetic fibres. Prolonged outdoor exposure causes degradation that significantly reduces breaking strength.
The fibre does not absorb water and retains its full strength in wet conditions.
How was the breaking strength of 8mm polypropylene rope measured?
The 8mm polypropylene rope during the test
Tests were carried out on a universal testing machine using rope-specific clamps (wedge or capstan type). The rope was loaded to break at a test speed of 20 mm/s, in accordance with the standard method for ropes up to 12mm diameter.
5 repetitions were performed. Results were measured dry, without pre-tension.
The clamps are specifically designed for fibre rope and prevent the rope from breaking at the clamp rather than in the free mid-section.
All five break points were assessed for location and failure mechanism. The average, highest, and lowest values are reported in accordance with the procedure used in this laboratory.
Tests were conducted in accordance with ISO 2307:2019.
Important for interpretation: this rope is 10 years old and was poorly stored. This is part of the test context and is decisive for comparison with other PP rope of the same diameter.
Breaking strength of 8mm polypropylene rope: test results
The five tests produced the following results:
- Average breaking strength: 7.99 kN (814 kg)
- Highest measured value: 8.30 kN
- Lowest measured value: 7.66 kN
- Number of tests: 5
The spread between the highest and lowest value is 0.64 kN — a relatively modest range for rope that has not been kept under controlled storage conditions. This suggests that degradation occurred fairly uniformly throughout the rope.
What stands out about this result: 7.99 kN is considerably higher than the average of 5.68 kN typically measured for 8mm PP rope.
At the same time, comparison with test result T-5646 — a better-stored specimen of the same rope type — shows a difference of nearly 200 kg.
Storage conditions therefore have a measurable and significant effect on the residual breaking strength after 10 years.
Poor storage costs approximately 200 kg of breaking strength; good storage reduces that loss considerably.
8mm polypropylene rope compared to other ropes
The figures below are averages from Prorope tests on ropes of comparable diameter (8mm). They provide context for the result of this specific rope:
- Polypropylene: 10.57 kN
- Polyester sheath-core braided with twisted core (all loose fibres): 10.17 kN
- Polypropylene 3-strand twisted: 9.91 kN
- This rope (10 years old, poorly stored): 7.99 kN
The tested specimen is therefore 1.92 kN (approximately 196 kg) below the average for new 3-strand twisted polypropylene rope of the same diameter.
Compared to new polypropylene (all constructions combined, 10.57 kN), the difference is 2.58 kN. These are not negligible margins — particularly when the rope is used for safety-critical tasks.
For applications where breaking strength is the deciding factor, fresh polyester sheath-core rope or new polypropylene performs considerably better at the same diameter.
When is 8mm polypropylene rope the right choice?
8mm 3-strand twisted polypropylene rope is best suited to applications where low cost, buoyancy, and sufficient strength for temporary use are the deciding factors. Specifically:
- Floating barriers and marker lines — PP floats, preventing it from becoming entangled in propellers or floating objects
- Temporary bundling of loads in agriculture — short service life, no extreme loading
- Internal logistics and storage — not exposed to prolonged UV radiation
- Pull lines and guide ropes where the load remains well below the working load, such as cable pulling
For this specific ten-year-old rope, an additional limitation applies: the breaking strength of 7.99 kN has been measured, but the working load must be determined accordingly using a safety factor of at least 5:1, which equates to a working load of approximately 160 kg (1.60 kN).
That is acceptable for light tasks, but marginal for more intensive use.
When is polypropylene rope not suitable?
Polypropylene rope — and certainly an old or poorly stored specimen — is unsuitable in the following situations:
- Prolonged outdoor exposure without protection: PP has the lowest UV resistance of all common synthetic fibres. Visible degradation (discolouration, crumbling surface) indicates reduced strength.
- Safety-critical applications: for lifting persons, fall protection, or lifting work, PP — and certainly aged rope — is not suitable. Use nylon or polyester with a certified MBL.
- High dynamic loads: PP has low energy absorption under shock loading. Impact loads are poorly dampened.
- High temperatures: PP has a low melting point. Friction or heat (>80°C) causes rapid damage.
- Rope with an unknown storage history: as this test demonstrates, residual strength after 10 years can be reduced by nearly 200 kg. Never use such rope without a current test or visual inspection.
Alternatives
Where higher breaking strength, better UV resistance, or longer service life is required at 8mm diameter, the following options are worth considering:
- Polyester braided 8mm black per metre — average 10.17 kN in Prorope tests; better UV resistance and minimal water absorption. Suitable for marine, rigging, and long-term outdoor use.
- Nylon braided (polyamide) (8mm, price per metre, white) — higher elongation (20–35% at break), resulting in significantly better shock absorption. Ideal for anchor lines and tow ropes. Note: nylon loses 10–15% strength when wet.
Conclusion
This 10-year-old, poorly stored 8mm polypropylene rope achieves an average breaking strength of 7.99 kN (814 kg) — notably high for its age, but measurably lower than comparable new rope due to storage conditions.
It is best suited to temporary, non-safety-critical applications where buoyancy and low cost are the deciding factors, and where the load remains well below the working load of approximately 160 kg.
For applications requiring continuity, UV resistance, or higher safety margins, fresh polyester or nylon rope is the better choice.
This test was carried out by Otto Tromm, who remains surprised that a decade-old, poorly stored rope pulls more than most people expect — but readily concedes that proper storage saves you nearly 200 kg of breaking strength.
Test data were collected by Prorope. This text was generated with AI on the basis of those data and verified for factual accuracy. Read how we test and publish →