1.7 MM BLIND CORD TESTED 102 kg for a cord as thin as a straw
Thin blind cord looks fragile, but held up to more than expected in the test. We pulled five pieces to breaking point to find out how much.
This 1.7 mm blind cord breaks at an average of 1.00 kN, or 102 kg.
You'd expect such a thin cord to handle very little tensile force. After all, it's thinner than a drinking straw and mainly used to raise and lower blinds. Yet this 1.7 mm blind cord withstood an average of 102 kg in the test before breaking. For a cord of this thickness, that's a solid result.
The five measurements were close together: between 0.94 kN and 1.07 kN. That's a spread of only 0.13 kN. The tensile force curve was somewhat erratic, with small fluctuations during the pull. According to the test notes, there were no significant dips.
Buying 1.7 mm polyester blind cord
This cord is made of polyester and has a core with sheath: a strong core of twisted fibres protected by a braided outer layer. This sheath protects the core against wear and, in a core-sheath construction, itself carries 30 to 50 percent of the load. Polyester absorbs almost no water and therefore loses almost no strength when wet.
This cord is part of our Interior rope collection. Polyester offers a good balance of strength, durability and price, with excellent wear resistance. View the 1.7 mm blind cord in the webshop.
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 used with this machine, selected depending on the diameter and material of the rope. These clamps allow rope to be tested without first having to be spliced.
All tests are carried out according to the ISO 2307:2019 guidelines. Among other things, this means testing is repeated 5 times at a test speed of 20 mm per minute. Each rope is secured so that it sits taut. No pre-tension is applied, since elongation is not measured in these tests.
Two repetitions of each test are filmed with a Sony camera on a tripod. The exact progression of the graph is also recorded separately on video.
This allows the tension progression and break behaviour to be matched exactly to the graph from the testing machine. For each of the 5 tests, the tester also records written observations, capturing details such as the degree of elongation, the way the rope breaks, and how loud the snap is when the rope fails.
Breaking strength test results
Five pieces of cord were tested to failure. The results were close together: the spread remained limited to 0.13 kN.
The curve was somewhat erratic, with small peaks and dips during the pull. There were no significant dips in the curve. Little comparative data is currently available for cord of this diameter, so firm conclusions about how it compares to other thin cords cannot yet be drawn.
How does this cord compare to other ropes
No other cord has yet been tested at exactly this diameter. However, the same blind cord has been measured at 2.5 mm, and the 1.5 mm Kevlar cord with polyester sheath is closest in thickness.
The 2.5 mm blind cord achieved an average of 1.29 kN (131 kg). The 1.5 mm Kevlar cord with polyester sheath came in at 1.05 kN (107 kg). At 1.00 kN (102 kg), this 1.7 mm cord is thus close to the thinner Kevlar cord.
When to use this blind cord
This cord is designed for light, repeated indoor operation. It is not intended as rope for heavy-duty tasks.
✓ Suitable for
- Operating blinds — the cord smoothly raises and lowers the slats, including daily use
- Pleated curtains — suitable for operating the curtain via a pull mechanism
- Replacement cord for existing blinds — at 1.7 mm, a thin cord for light indoor operation
✕ Not suitable for
- Carrying weight — 102 kg is the breaking strength measured in a test, not a guideline for hanging something
- Outdoor use — the cord has not been tested for UV or weather resistance for outdoor applications
- Heavy curtains or roller blinds — with a measured breaking strength of 1.00 kN, this cord is intended for light loads
- Climbing or safety applications — this cord is never intended for supporting people
Conclusion: strong enough for its intended purpose
In the test, this 1.7 mm blind cord achieved an average of 1.00 kN, or 102 kg, with a small spread of 0.13 kN across the five measurements. That's more than enough for operating blinds and pleated curtains. Do not use it for anything other than light indoor operation — that's not what this cord is designed for.
Otto Tromm broke this cord five times and concluded that the blinds at his own home are probably attached more securely than strictly necessary.