Testing standard
Footwear — Test methods for uppers — Tensile strength and elongation
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ISO 17706 determines the force required to break a test specimen taken from a footwear upper, irrespective of the material it is made from, together with the tensile elongation. Jaws are set 100 mm apart and separate at 100 mm/min. The current edition is ISO 17706:2003, confirmed on review in 2021 and republished in Europe as EN ISO 17706:2018.
A rectangular strip cut from a footwear upper is clamped with the jaws 100 mm ± 1 mm apart and pulled at 100 mm/min ± 5 mm/min until it fails. Both the breaking force and the tensile elongation are taken from the same pull. The strip is marked with two lines 100 mm ± 1 mm apart before mounting, and those lines are aligned with the clamping edges of the jaws, so the operator can see afterwards whether the specimen crept out of the grips during the test rather than stretching in the gauge.
Whether the upper is strong enough for the job, whatever it is made of. The scope is written around the component rather than the material — leather, coated textile, woven textile and laminate all go through the same procedure — because a shoe designer choosing between them needs numbers produced the same way. The method also allows the complete upper assembly to be tested: the finished, seamed, lined construction including interlinings, adhesives, membranes, foams and reinforcements, but excluding toe puffs and stiffeners. That distinction is the useful part. A lining permanently attached to the outer material changes what the upper does, and testing the outer alone describes a material the shoe does not contain.
Two preparation routes, decided by whether the material frays. Both end at the same 25 mm test width, and the route taken has to be right for the material.
Where a shoe is too small to yield a full-size specimen — children's footwear especially — the specimen size shall not be reduced. The materials themselves are tested instead.
The maximum tensile stress recorded in extending the specimen to breaking point
The method's own definition. The width of every specimen is measured and recorded to 0,5 mm, which is why the width matters even though every specimen is nominally 25 mm.
The tensile strain in the test length at breaking
Along and across reported separately
Three specimens in each direction. Uppers are anisotropic whether they are leather, coated fabric or textile, and a single figure hides which way the weakness runs.
The rejection rule has an exception that matters: if three specimens cut in the same direction all fail within 5 mm of a jaw, the results are not rejected. At that point the failure position is a property of the material rather than a grip problem.
A 25 mm specimen width with a 100 mm gauge, held at a constant clamping pressure. The standard's own footnote makes the point: the clamping force and jaw type must suit the specimen, because slipping and failure at the clamping edge are what invalidate the test.
Specifications
The force range has to be chosen for the material. The standard states it will usually be under 1 kN for textile and coated textile uppers, but may be as high as 5 kN for thick leathers — leather over 2 mm.
SpecificationsA modest frame, precisely controlled. Jaw separation must run at 100 mm/min ± 5 mm/min, and the force-measuring system must be accurate to better than 2 %, which the standard states as class 2 of EN ISO 7500-1. The force range has to suit the specimen: the standard notes it will usually be under 1 kN for textile and coated textile upper materials, but may reach 5 kN for thick leathers, meaning leather over 2 mm. The clamping force and jaw type must be chosen for the material, because the specimen has to be held without being cut or crushed at the clamping edge.
Grip failures, mostly, and the standard is unusually specific about them. If a specimen slips asymmetrically by more than 2 mm, or fails within 5 mm of either jaw, the result is rejected and the test repeated on fresh pieces — but if three specimens cut in the same direction all fail within 5 mm of a jaw, the results are not rejected, because at that point the failure is telling you something about the material rather than the grip. Beyond that: skipping the fraying step on a textile and testing a 35 mm strip; cutting a specimen smaller to make it fit a child's shoe, which the method forbids outright and answers by saying test the materials instead; and testing the outer material when the lining is permanently attached to it.
| ISO 17706 | ISO 17708 | ISO 23910 | |
|---|---|---|---|
| Subject | A strip cut from the upper | The finished shoe | A slit test piece of leather |
| Measures | Breaking force and elongation of the upper | Upper to sole adhesion | Force to tear leather away from a stitch hole |
| Fails at | The material, in tension | The bond between upper and sole | The leather between hole and edge |
| Speed | 100 mm/min ± 5 mm/min | A constant rate of separation as specified | 100 mm/min ± 20 mm/min |
Three separate failure modes on the same shoe. A strong upper says nothing about the sole bond, and neither says anything about whether the seams will hold.
ISO 17706 specifies a test method for determining the force required to break a test specimen taken from a footwear upper, irrespective of the material, in order to assess its suitability for the end use. The tensile elongation is measured in the same pull. The current edition is ISO 17706:2003, the first, confirmed on systematic review in 2021.
Because an upper is not always leather, and often is not only leather. ISO 17706 is written around the component: textile, coated textile, laminate and leather uppers all go through the same procedure, so the numbers can be compared when a designer is choosing between them. The method descends from IULTCS/IUP 6 and the 1976 edition of ISO 3376, which is where its 100 mm gauge and 25 mm width come from.
It is the finished upper — fully seamed, joined or laminated, comprising the centre material and any linings together with interlinings, adhesives, membranes, foams and reinforcements, but excluding toe puffs and stiffeners. It is tested rather than the outer material alone when the lining is permanently attached, because at that point the outer material on its own is not something the shoe contains.
So the 25 mm test width is made of whole yarns rather than cut ones. A textile cut straight to 25 mm has severed yarns along both edges that carry no load and shed no load into their neighbours, which lowers the result and raises its scatter. Cutting at 35 mm and removing threads from both edges until the width is 25,0 mm ± 0,5 mm leaves a specimen whose edges are the natural ends of continuous yarns.
If a specimen slips asymmetrically in the jaws by more than 2 mm, or fails within 5 mm of either jaw, the result is rejected and the test repeated with fresh specimens. There is one exception, and it is important: if three specimens cut in the same direction all fail within 5 mm of a jaw, the results are not rejected. Consistent failure near the jaws is behaviour of the material, not evidence of a gripping problem.
The jaws start 100 mm ± 1 mm apart and separate at 100 mm/min ± 5 mm/min. The two lines marked on the specimen are also 100 mm ± 1 mm apart and are aligned with the clamping edges when the specimen is mounted, so after the test the lines show whether the specimen crept out of the jaws instead of stretching between them.
The standard asks for force measurement to better than 2 %, stated as class 2 of EN ISO 7500-1. The force range must suit the specimen: usually less than 1 kN for textile and coated textile upper materials, but potentially as high as 5 kN for thick leathers, which the method defines as leather over 2 mm.
The specimen is not made smaller. The method notes explicitly that it may not be possible to cut a specimen of sufficient size from certain footwear, especially children's, and says the specimen size should not be reduced — the materials themselves are tested instead. A shortened specimen has a different gauge length and is not comparable with anything.
In content, yes. ISO 17706 was prepared by CEN as EN 13522:2001 and adopted by ISO/TC 216 under a fast-track procedure, which is why the published ISO text carries the EN clause numbering alongside the ISO reference. CEN has since republished the same technical content as EN ISO 17706:2018. Quote the designation the specification asks for.
Dak verifies against whichever standard the method names, and where a class applies our frames sit a class tighter than it asks.
| The method asks for | Dak supplies | |
|---|---|---|
| Capacity | Usually under 1 kN for textile and coated textile upper materials, but as high as 5 kN for thick leathers, which the method defines as leather over 2 mm | Load cells from 1 kg to 60 ton on the Series 7200, and 0.5 to 100 kN on the Series 9000 |
| Force accuracy | Better than 2 %, stated as class 2 of EN ISO 7500-1 | ISO 7500-1 Class 0.5 — a class tighter than the method asks |
| Gripping | Grips whose clamping force and jaw type suit the material, so it is neither cut nor allowed to slip | Wedge, vice-action, pneumatic and hydraulic grips, built to the specimen |
| Environment | The footwear standard atmosphere of EN 12222, for at least 48 h before the test and during it | 3009 series chambers, −150 °C to +400 °C — temperature only |
This page describes the method as practised. The governing text is the current edition from the issuing body. Tell us what you are testing and we will answer with the machine, the fixture and a quotation.
