FIGURE-EIGHT KNOT IN 5 MM HMPE: 73% strength retained
A figure-eight knot reduces strength less than expected — but the spread of 68% to 82% retention is wide enough to base every safety calculation on the lowest value.
A figure-eight knot in 5 mm HMPE blue/gold breaks at an average of 6.75 kN (688 kg) — that is 73% of the unknotted breaking strength of 9.27 kN (945 kg).
The common rule of thumb states that a knot in HMPE removes around 40 to 60 percent of the strength — and that an eye splice is preferable. That holds for a tight overhand knot, but the figure-eight knot performs noticeably better in this cord. Whether that "better" is sufficient for a given application depends on the lowest measured value, not the average.
Across five measurements, the breaking strength with a figure-eight knot ranged from 6.29 kN to 7.63 kN, a spread of 1.34 kN. That variation translates to a retention range of 68% to 82% of the unknotted breaking strength.
In two of the five cases the cord broke in a single continuous pull; the remaining measurements showed a staged load build-up. The average (73%) indicates the trend — but a user should statistically allow for the lower end: 68%.
UHMWPE cord 5 mm blue/gold — braided core with sheath
The 5 mm HMPE cord blue/gold is constructed as a braided core with sheath (kernmantle construction). The HMPE core provides the breaking strength; the braided sheath protects against abrasion and keeps the core aligned.
Without a knot, this rope breaks at an average of 9.27 kN (945 kg) over five measurements from 18 December 2025. HMPE does not absorb water and retains its strength when wet — relevant for marine and outdoor applications.
This rope is part of our HMPE rope collection.
How we test with a figure-eight knot
The 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 purpose-built rope clamps are available for this machine, selected based on the diameter and material of the rope. These clamps allow rope to be tested without requiring an eye 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 in such a way that it is 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 load curve is recorded separately on video. This allows the load profile and failure behaviour to be matched precisely to the graph from the breaking strength machine.
For each of the 5 tests, the tester also records observations in writing, capturing details such as the degree of elongation, the manner in which the rope breaks, and the loudness of the snap at the moment of failure.
For this test, the standard procedure was followed with one deviation: a figure-eight knot was tied in the rope before it was placed in the clamps, and a soft shackle was used for the connection to the rope bracket below.
The machine, clamps, test speed, and the number of 5 measurements are identical to a test without a knot, so that any difference in measured breaking strength can be attributed to the figure-eight knot. The reference value without a knot comes from an earlier test of the same rope (5 measurements, 9.27 kN).
A spread of 68% to 82% retention means: the same knot, the same hands, yet a 1.34 kN difference. Always use the lower end.— from testing practice
Test results: figure-eight knot in 5 mm HMPE
Five measurements, test speed 20 mm/min.
The average breaking strength with a figure-eight knot is 6.75 kN (688 kg). The spread from 6.29 kN to 7.63 kN (a difference of 1.34 kN) is considerable for an identical test setup.
This is characteristic of knot tests: the exact position and tightness of the knot visibly influence the result.
Retention averages 73% relative to the unknotted baseline of 9.27 kN.
The lowest measurement gave 68% retention, the highest 82%. Safety margins must be calculated from the 68% figure — that is 6.29 kN (approximately 641 kg). In three of the five measurements the cord broke in a single continuous pull; in the remaining two, failure was staged.
The reported values are in all cases the load at which the knotted connection failed.
Comparison: the same rope in three knot variants
The comparison bar shows the same 5 mm HMPE blue/gold rope in four conditions: unknotted, with a previously unspecified knot, with a bowline, and with the figure-eight knot tested here.
The bars therefore compare not different products, but one rope in different knotted conditions.
Unknotted: 9.27 kN (baseline). Unspecified knot (18 Dec): 4.83 kN — 52% retention. Bowline (13 Aug): 5.58 kN — 60% retention. Figure-eight knot (current test): 6.75 kN — 73% retention. The figure-eight knot clearly retains more strength than both previously tested knot variants.
Alternatives to knotted connections in 5 mm rope
Conclusion: figure-eight knot outperforms other knot variants
A figure-eight knot in 5 mm HMPE blue/gold retains an average of 73% of the unknotted breaking strength (6.75 kN / 688 kg) against a baseline of 9.27 kN.
That is better than the previously tested bowline (60%) and unspecified knot (52%). The practically relevant lower limit is however 68% — 6.29 kN: that is the figure on which safety margins must be based.
For temporary, low-load or non-safety-critical connections, the figure-eight knot is an acceptable choice.
Otto Tromm tied five figure-eight knots, pulled them to failure, and concluded he is better at tying knots than at spreadsheets — though the average came out exact this time.