HMPE 3 MM WITH SHEATH: 2.13 kN — weaker than expected
An HMPE core with a polyester sheath sounds like a strong combination. The test results tell a different story: an average of 218 kg, well below the average for 3 mm HMPE.
This 3 mm HMPE cord with polyester sheath and blue marker thread broke at an average of 2.13 kN (218 kg) — notably lower than the average of 3.06 kN measured for comparable 3 mm HMPE cord.
HMPE — also known as Dyneema — is recognised as the strongest rope fibre per unit weight available. A 3 mm cord with an HMPE core and a polyester sheath should therefore perform impressively on paper. Assuming that without knowing the numbers, however, can lead to surprises.
Across five measurements, the breaking strength ranged from 2.07 kN to 2.18 kN, a spread of just 0.11 kN. That is consistent — but consistently low.
More notable was the behaviour during testing: the cord did not break completely in a single loading cycle on any of the five tests.
The second break only occurred after restarting the testing machine. This behaviour is unusual for HMPE and suggests that the polyester sheath and the HMPE core do not fail simultaneously.
The material
This cord combines an HMPE core (High-Modulus Polyethylene) with a braided polyester sheath and is identifiable by its blue marker thread.
The polyester sheath provides protection against UV and abrasion; the HMPE core supplies the tensile strength. HMPE has an inherent elongation of less than 4% at break and does not absorb water — wet strength is equal to dry strength.
In a double-sheath construction, the polyester sheath typically carries 30–50% of the load, which contributes to the overall breaking strength.
This rope is part of our HMPE rope collection.
How we test
Breaking strength tests are carried out in-house by Otto Tromm on a universal testing machine with a capacity of 50 kN.
Two sets of specially developed rope clamps are available for this machine, selected based on the diameter and material of the rope being tested. These clamps allow rope to be tested without requiring a splice beforehand.
All tests are conducted in accordance with the guidelines of ISO 2307:2019. This includes testing five times and using a test speed of 20 mm per minute.
Each rope is secured so that it sits taut. No pre-tension is applied, as elongation is not measured in these tests.
Each test is filmed from two angles using a Sony camera on a tripod. In addition, the exact progression of the graph is recorded separately on video.
This allows the load curve and break behaviour to be matched precisely with the graph from the testing machine.
For each of the five tests, observations are also recorded in writing by the tester, capturing details such as the degree of elongation, the manner in which the rope breaks, and the intensity of the snap when the rope fails.
It did not break completely on a single loading cycle — the final break only occurred after restarting the test.— from the test observations, 3 mm HMPE with polyester sheath
Test results: 2.13 kN average over 5 measurements
The spread across the five measurements was 0.11 kN — from 2.07 kN (lowest) to 2.18 kN (highest). This indicates a consistent production process. Uniformity is good; the level itself is notably low for a 3 mm HMPE cord.
The most notable finding was not the figure itself, but the break behaviour: the cord did not break completely in a single loading cycle on any test.
The final break only occurred after restarting the testing machine. This indicates that the HMPE core and the polyester sheath fail at different moments — a phased break rather than a simultaneous one.
For applications where a sudden, complete failure is the worst-case scenario, this behaviour may be relevant. The measured average of 2.13 kN is approximately 30% below the average of 3.06 kN recorded in our series for 3 mm HMPE cord.
Comparison with other 3 mm cords
For reference: at the same diameter and using the same test method, the following average breaking strengths were measured. The differences are significant.
Kevlar 8-strand braided scores highest at 5.85 kN — 2.7× more than this HMPE sheath cord. Dyneema SK78 (without sheath) measures 5.16 kN.
Nylon braided achieves 2.90 kN — that is 0.77 kN more than this HMPE sheath cord, at the same diameter.
The fact that nylon, a material with a lower intrinsic fibre strength than HMPE, scores higher here underlines that the construction and sheath ratio of this specific product are a limiting factor.
When it is suitable — and when it is not
A breaking strength of 2.13 kN at a safety factor of 5:1 yields a working load of approximately 43 kg. This largely determines the applications for which this cord is appropriate.
✓ Suitable for
- Marking and identification — the blue marker thread makes this cord suitable as a colour-coded identification line in bundles or systems.
- Light lashing applications — at loads well below 40 kg, the polyester sheath provides protection and the HMPE core delivers minimal elongation.
- Marine (non-critical) — as a fender line, marker thread, or auxiliary line where high tensile loads do not occur.
- Instrumentation applications — suspending light sensors or equipment where elongation (<4%) is a requirement.
✕ Not suitable for
- Safety-critical lifting applications — 43 kg working load (at 5:1) is too low for most professional lifting situations.
- Prolonged static loading at elevated temperatures — HMPE creeps at temperatures above 60°C; not suitable for permanent static loads in warm environments.
- Replacement of full HMPE rope on breaking strength grounds — where the full capacity of HMPE is required, a cord without sheath or a larger diameter is the better choice.
- Shock loading — elongation <4% at break means virtually no energy absorption; unsuitable as a tow line or anchor line.
Alternatives for higher strength requirements
Conclusion: consistent, but weaker than expected
The 3 mm HMPE cord with polyester sheath and blue marker thread performs consistently — spread of 0.11 kN across five measurements — but at 2.13 kN average it falls well short of what the HMPE fibre promises on paper. The phased break behaviour (no complete break on the first loading cycle) and the low result relative to the reference value of 3.06 kN make this cord unsuitable for applications where the full HMPE capacity is required.
Best application area: marking, light auxiliary lines, and non-critical marine applications where minimal elongation and the protective sheath do add value.
3mm HMPE with polyester sheath and blue marker thread
View this rope on prorope.eu →Otto Tromm had estimated this cord to be stronger. After the fifth measurement — and restarting the testing machine twice — he revised that assessment. The numbers are now on record, and Otto is still slightly surprised by them.