Editor: Otto Tromm | Test date: 11-4-2026
A Kevlar cord of 1.5 mm is thin — thinner than a pencil tip. What this cord does under a tensile test, and how it compares to a thicker variant, makes this a notable test result.
What is the breaking strength of the 1.5 mm Kevlar cord with polyester sheath?
In our test, the cord broke at an average of 1.05 kN (107 kg), based on 5 measurements.
The highest measured value was 1.10 kN, the lowest 0.98 kN.
What type of cord is this?
This is a 1.5 mm cord with an aramid (Kevlar) core and a braided polyester sheath.
The construction is functional: Kevlar provides the tensile strength, while polyester protects the core against UV radiation and mechanical wear.
Without a polyester sheath, Kevlar degrades rapidly when exposed to sunlight. The sheath significantly extends the usable service life.
This construction type is used in applications where a very small diameter must be combined with high tensile strength, such as in optical instruments, kite surfing auxiliary lines, rescue equipment, technical modelling, and industries where weight and space are limiting factors.
The cord is not elastic. Kevlar has an exceptionally low elongation at break — typically less than 4% — meaning it absorbs virtually no energy under shock loading.
It is intended for static or near-static applications.
Test method
The test was carried out on a universal testing machine with rope-specific clamps, suitable for measuring cord without splices. The test speed was 20 mm/s. Five repetitions were performed on separate lengths of the same cord.
No pre-tensioning or pre-loading was applied prior to measurement.
The measured values represent the breaking strength of the cord as supplied, without knots or connections.
The tests were conducted as closely as possible in accordance with ISO 2307:2019, the most recent version of this standard.
Results
Based on 5 tests, an average breaking strength of 1.05 kN (107 kg) was measured. The highest measured value was 1.10 kN, the lowest 0.98 kN.
The spread between measurements is small: the difference between the highest and lowest value is only 0.12 kN.
A notable pattern was observed during testing. The first break was unusually gradual — the cord yielded progressively rather than failing abruptly.
In the four subsequent tests, the break behaviour was much more consistent: four measurements recorded 0.82 kN and one recorded 0.78 kN at the second break point per measurement.
This indicates a reproducible break pattern in the core following initial failure of part of the construction.
The most notable aspect of this result is the comparison with 2 mm Kevlar cord with polyester sheath.
The average difference in breaking strength between 1.5 mm and 2.0 mm is only approximately 10 kg. For a diameter difference of 0.5 mm, that is a remarkably small margin.
Comparison with similar cords
No comparative data from other cords with exactly the same diameter are available for this product.
What is notable: the 1.5 mm Kevlar cord performs closer to 2 mm Kevlar than would be expected based on diameter alone.
This makes the 1.5 mm cord particularly relevant where space or weight is the deciding factor, but the strength result is nearly equivalent.
When should this cord be used?
This cord is best suited for applications where a very small diameter is essential and a tensile strength of around 100 kg is still required. Examples include:
- Technical auxiliary lines in rescue or survival equipment where weight and space are limited
- Connection cords in instruments or equipment with narrow passages
- Kite surf or kite auxiliary lines where zero elongation is required
- Industrial applications with limited space for a thicker cord
- Scale modelling and technical applications requiring high tensile strength per mm²
The cord is best suited for static loading without shock, in a sheltered environment or outdoors with adequate protection from the polyester sheath.
Limitations
This cord is not suitable for applications involving shock loading. Kevlar has an elongation at break of less than 4%, meaning a sudden force impulse is not absorbed but leads directly to failure.
For shock absorption, materials such as nylon (20–35% elongation) are considerably more appropriate.
The cord is also not suitable for use with clamps or knots under high load. Knots reduce breaking strength by 35–55%, bringing the effective strength down to 50–70 kg depending on knot type.
Under repeated bending or bending fatigue, Kevlar loses significant strength. This cord is therefore not intended for dynamic or running applications such as winches, pulley systems, or frequently moving connections.
The polyester sheath protects the core against UV, but does not provide full protection under prolonged outdoor exposure. Inspect the sheath regularly for wear or damage, as a damaged sheath means direct UV exposure of the sensitive aramid core.
Alternatives
Polyester cord 1.5 mm: For applications where some elongation is acceptable (10–15% at break) and UV resistance is a priority, a polyester cord of comparable diameter is a practical alternative. Breaking strength is lower, but the cord handles dynamic loading and bending fatigue better.
HMPE / Dyneema cord 1.5 mm: For maximum strength per mm² with equally minimal elongation, HMPE is an alternative.
HMPE is lighter than Kevlar, does not absorb water, and has higher bending fatigue resistance. The drawback: HMPE creeps under sustained loading at elevated temperatures (above 60°C) and has no inherent UV protection without a sheath.
Conclusion
The 1.5 mm Kevlar cord with polyester sheath delivers an average breaking strength of 1.05 kN (107 kg) at an exceptionally small diameter, making it suitable for technical applications where space and weight are critical.
The narrow margin of only 10 kg relative to 2 mm Kevlar makes this cord particularly efficient for its diameter, provided it is used in static situations without shock or bending loads.
This test was carried out by Otto Tromm, who still cannot explain why a 1.5 mm cord is almost as strong as a 2 mm one — but is convinced the universal testing machine was equally surprised.
Test data collected by Prorope. This text was generated with AI on the basis of that data and verified for factual accuracy. Read how we test and publish →