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ISO 11339
T-Peel Test of Flexible-to-Flexible Adhesive Bonds

Universal Grip ISO 11339 t-peel fixture with pneumatic grips

Downloads: ISO 11339 T-Peel Fixture with Pneumatic Grips – Universal Grip Data Sheet (PDF)

Written by Chris Thomas, Universal Grip Company · Reviewed by Frank Bertini · Updated October 24, 2026

ISO 11339 is the international T-peel test for adhesive bonds between two flexible adherends. Two thin strips, typically 0.5 mm steel or 0.7 mm aluminium, are bonded face to face over 150 mm, their free ends are bent apart to form a T, each leg is clamped in a grip and the crosshead separates them at 100 mm/min while the force is recorded. The average force over the middle of the peel, divided by the width, is the peel resistance in newtons per 100 mm of width. It is the ISO counterpart of ASTM D1876, and it is the standard test for sheet-metal bonding in automotive bodies, foil and laminate packaging, flexible electronics and any joint where both adherends can bend.

This guide covers the current edition, ISO 11339:2022, and the unit and terminology changes from the 2010 and 2022 revisions; the specimen geometry with the 200 mm strip, 150 mm bond and 50 mm legs, the preferred adherends, and the panel-and-edge-strip rules; grips that hold the outer 25 mm of each leg and the question of which leg goes in the moving grip; the 100 mm/min and 10 mm/min rates and the 2:1 relationship between crosshead travel and peeled length; the evaluation window that discards the first and last 25 mm; the calculation with worked examples and every unit conversion; ISO 10365 failure codes; common errors; a numeric comparison with ASTM D1876, ISO 8510-2 and ASTM D903; and the fixture, grips and machines Universal Grip supplies. The peel testing application page and the peel fixtures page give the lab overview and the ISO standards hub lists every ISO method we equip.

In this guide: What ISO 11339 Measures and Where It Applies · Editions: 1993, 2003, 2010 and 2022 · The Specimen: 25 mm Strips, 150 mm Bond, 50 mm Legs · Grips, Alignment and Which Leg Moves · Speed, Peel Length and the 2:1 Rule · Step-by-Step ISO 11339 Procedure · Calculation, Units and a Worked Example · Failure Modes Under ISO 10365 · Common Errors and How Much They Cost · ISO 11339 vs ASTM D1876, ISO 8510-2 and ASTM D903 · Equipment: T-Peel Fixture, Grips and Machines for ISO 11339 · Report Checklist · FAQ

What ISO 11339 Measures and Where It Applies

ISO 11339 determines the peel resistance of an adhesive from the force needed to separate a T-shaped assembly of two flexible adherends. Because both adherends bend, the angle between the bond line and the applied force is not fixed by a fixture: the legs settle at roughly 180° to each other and the peel front runs along the bond at half the crosshead speed. The standard was written for metal adherends and allows any flexible adherend, defined as one that can bend through 90° without cracking, so it covers thin steel and aluminium, foils, laminates, coated fabrics and flexible plastics bonded to the same or a similar material.

  • Reported property: peel resistance, the average peeling force over a defined length divided by the specimen width, in newtons per 100 mm of width, together with the maximum and minimum force and the ISO 10365 failure pattern.

  • What it is for: comparing adhesives, surface preparations and cure schedules, QC of bonded sheet-metal and laminate joints, and screening flexible-to-flexible bonds before design.

  • What it is not for: design values, since the result depends on the adherend thickness and stiffness as much as on the adhesive; flexible-to-rigid bonds, which go to ISO 8510-1 (90°) and ISO 8510-2 (180°); and pressure-sensitive tapes, which use ISO 29862 and the tape standards.

A T-peel number is only comparable between labs when the adherend material and thickness match, because a thicker arm absorbs more energy in plastic bending as it peels; this is why the standard names preferred adherends and requires the thickness in the report.

Editions: 1993, 2003, 2010 and 2022

ISO 11339:2022 is the fourth edition and is a minor revision of the 2010 third edition. The first edition of 1993 and the second of 2003 reported peel strength in kN/m; the 2010 edition changed the reported quantity to newtons per 100 mm of width, which is why older certificates and most competitor pages still show kN/m or N/mm. The 2022 edition renamed 'peel strength' to 'peel resistance' to reflect that the value is a force per width, not a stress, and replaced the surface-preparation reference EN 13887 with ISO 17212. The specimen, rates and evaluation window have not changed since 2003.

The normative references are ISO 291 for the conditioning atmosphere, ISO 10365 for failure-pattern designation and ISO 17212 for surface preparation of metals and plastics. ISO 6133, the method for averaging multi-peak traces, is used by the tape and tear standards but is not referenced by ISO 11339; the standard's own averaging rule is a best straight line through the trace, and a peak-counting analysis is a related practice that must be declared, not the default. The standard states that no precision data are available.

The Specimen: 25 mm Strips, 150 mm Bond, 50 mm Legs

The specimen is a pair of flexible strips bonded over most of their length with the ends left unbonded to form the legs of the T. The standard figure gives the following geometry, and other widths are permitted if they are reported.

  • Width: 25 mm, the width the grips are built for; the result is normalised to 100 mm so the width is measured and reported on each specimen.

  • Overall length: about 200 mm, made up of a bonded length of at least 150 mm and unbonded legs of 50 mm at one end.

  • Preferred adherends: steel 0.5 ± 0.02 mm (deep-drawing grade) or aluminium 0.7 ± 0.02 mm or 0.5 ± 0.02 mm (5754 H111), unless the material specification says otherwise; the material and thickness are always reported.

  • Panels: specimens are normally cut from a bonded panel of 150 × 200 mm into six 25 mm strips; the two outer strips are labelled edge specimens and reported separately, because adhesive squeeze-out and pressure variation at a panel edge change the result.

  • Adhesive layer: not fixed by the standard; measured on each specimen to ± 0.01 mm with a thickness gauge and reported as the average.

  • Forming the T: the unbonded ends are bent in opposite directions through 90° to the bond plane, at the end of the bond, so that each leg presents a straight 50 mm length to its grip.

Surface preparation follows ISO 17212 and the adhesive manufacturer's instructions, cure follows the adhesive schedule, cutting must not damage the bond (a guillotine that bends the strips will pre-peel the edge), and the specimens are conditioned in the ISO 291 standard atmosphere of 23 ± 2 °C and 50 ± 10 % relative humidity and tested in the same atmosphere. At least five specimens are tested; edge specimens do not count toward the five unless reported as such.

Grips, Alignment and Which Leg Moves

The machine must hold a constant crosshead rate, read force to within 2 % and record force against crosshead movement; a thickness gauge reading to 0.01 mm completes the apparatus. The grips are self-aligning and each set of jaws holds the outer 25 mm of one unbonded leg, so that the 50 mm leg is half in the jaw and half free. Low-inertia clamping is recommended because T-peel forces on thin metal are small, often 10 to 100 N on a 25 mm strip, and a heavy swinging grip adds noise of the same order.

  • Equal clamping: the two legs must be clamped with the same pressure and aligned across the width, otherwise the T twists and the peel front runs at an angle, which raises the force on one edge and lowers it on the other.

  • Stiffer leg in the moving grip: when one adherend is less flexible than the other, the standard's long-standing instruction is to put the less flexible adherend in the moveable grip so that the compliant leg feeds through the stationary side; check the clause in your edition and record which way round the specimen was mounted.

  • Jaw faces: flat or lightly serrated faces for 0.5 mm steel and aluminium; rubber or coated faces for foils and laminates that a serration would cut.

  • Tail support: the bonded section hangs below the grips and, with long metal strips, its weight and swing add to the recorded force at low loads. A guided tail-support frame holds the bonded section between the grips for a supported peel; the choice of supported or unsupported peel is reported because it changes the result at low forces.

  • Data rate: peel traces are jagged; sample at 100 Hz or faster so that the maximum and minimum are real and the average is not biased by sparse sampling.

Speed, Peel Length and the 2:1 Rule

The separation rate is 100 mm/min for metal adherends and 10 mm/min for other adherends, held constant throughout the test. Because both legs move apart, each millimetre of crosshead travel peels only half a millimetre of bond: the peel front advances at 50 mm/min when the crosshead runs at 100 mm/min. The test continues until at least 150 mm of bond has separated, which is the whole bonded length of the standard specimen and takes about 300 mm of crosshead travel, three minutes at 100 mm/min or thirty minutes at 10 mm/min. Confirm that the frame has the stroke before buying a long-stroke clip-on gauge for nothing: 300 mm of travel plus the grip train needs a crosshead travel of roughly 500 mm.

  • Evaluation window: the first 25 mm and the last 25 mm of peel are disregarded and the force is evaluated over about 100 mm of peel in the middle, which is 50 mm, 200 mm and 50 mm of crosshead travel respectively on the chart.

  • Why the start is discarded: the initial peak at the end of the bond includes the force to bend the legs into the T and start the crack; it is not peel resistance.

  • Why the end is discarded: the last 25 mm of bond carries the specimen's own weight and the final tear-off.

  • Chart units: the machine records crosshead movement, so the windows must be set at twice the bond lengths; reporting crosshead millimetres as peel millimetres is the most common error in T-peel reports.

Step-by-Step ISO 11339 Procedure

  • Prepare: cut and prepare the adherends per ISO 17212, bond a 150 × 200 mm panel with the adhesive maker's method, pressure and cure, leaving 50 mm unbonded at one end (masking tape or release film under the leg area).

  • Cut: six 25 mm strips with a method that does not bend or heat the bond; label the two edge strips; measure width and adhesive thickness on each.

  • Condition: ISO 291 atmosphere, 23 ± 2 °C and 50 ± 10 % RH, for the period the adhesive specification requires; test in the same atmosphere.

  • Form the T: bend each leg through 90° away from the other at the end of the bond.

  • Mount: clamp the outer 25 mm of one leg in the upper grip and the outer 25 mm of the other in the lower grip, aligned square across the width, with equal clamping pressure; fit or remove the tail support as the test plan states.

  • Run: 100 mm/min for metals (10 mm/min for other adherends) until at least 150 mm of bond has separated, recording force against crosshead movement.

  • Evaluate: on the trace, discard the first and last 25 mm of peel (50 mm of crosshead each) and draw the best straight line through the middle 100 mm of peel; read the average, maximum and minimum force in newtons.

  • Inspect: designate the failure pattern per ISO 10365 along the peeled length.

  • Calculate and report: peel resistance in N per 100 mm of width for each specimen, with average, maximum and minimum, the failure type and the report items below.

Calculation, Units and a Worked Example

Peel resistance is the average peeling force over the evaluated length divided by the specimen width and normalised to 100 mm: peel resistance (N/100 mm) = F_avg (N) × 100 / b (mm). The maximum and minimum forces over the same window are converted the same way and reported alongside.

  • Example: a 25.0 mm wide steel T-peel specimen gives a best-straight-line average of 42 N over the middle 100 mm of peel, with a maximum of 55 N and a minimum of 31 N. Peel resistance = 42 × 100 / 25 = 168 N/100 mm; maximum 220 N/100 mm; minimum 124 N/100 mm.

  • The same result in other units: 168 N/100 mm = 1.68 N/mm = 42 N/25 mm = 1.68 kN/m = 9.6 lbf/in. The conversions are: 1 N/mm = 100 N/100 mm = 25 N/25 mm = 1 kN/m = 5.71 lbf/in; 1 lbf/in = 0.175 N/mm = 17.5 N/100 mm.

  • Width matters: the same 42 N on a 24.6 mm strip is 171 N/100 mm, a 1.6 % difference, which is why width is measured on each specimen.

  • Averaging: the standard's method is the best straight line through the trace over the window; for stick-slip traces a peak-and-trough analysis in the style of ISO 6133 is a legitimate additional analysis but must be declared as such and reported separately.

Report each specimen and the set, keeping edge specimens separate, and quote the units exactly: a value in N/mm quietly read as N/100 mm is a factor of 100 error and it happens because the 2010 unit change is rarely mentioned.

Failure Modes Under ISO 10365

Each peeled specimen is inspected along its length and the failure pattern designated with ISO 10365 codes, because the force says how hard the joint was to peel and the pattern says what limited it.

  • CF, cohesive failure: adhesive on both faces along the peel; the result characterises the adhesive and is the mode datasheet values assume.

  • AF, adhesive failure: one face bare; the interface, usually the surface preparation, limited the result.

  • SCF, special cohesive failure: a thin adhesive film left on one face; a weak boundary layer or primer effect.

  • Mixed patterns: the percentage of each mode along the length, which often changes as the peel front runs from the panel edge inward.

  • Adherend failure or yielding: if a 0.5 mm leg necks or tears before the bond peels, the test is a floor on peel resistance and the adherend is too thin for that adhesive.

Common Errors and How Much They Cost

  • Averaging the initial peak: including the first 25 mm raises the average by 10 to 30 % on structural adhesives because the start-up peak includes bending the legs.

  • Crosshead millimetres reported as peel millimetres: evaluating 100 mm of crosshead travel instead of 100 mm of peel evaluates only 50 mm of bond, halves the sample of the trace and usually lands inside the discarded start region.

  • Mixing units: N/mm read as N/100 mm is a 100× error; kN/m from a 2003-era report equals N/mm, not N/100 mm.

  • Unequal clamping: one grip at 4 bar and the other at 6 bar twists the T; edge-to-edge force differences of 20 % are typical and the failure pattern becomes diagonal.

  • Bending the legs over a radius: a soft bend leaves a curved transition that peels first and adds a false peak; the legs are bent sharply at the end of the bond.

  • Too short a peel: stopping at 100 mm of separation leaves only 50 mm for the window after the discards; the standard needs at least 150 mm separated.

  • Edge strips in the mean: the two outer strips of a panel are reported separately; averaging them in biases the set by whatever the panel edge did.

  • Wrong rate for non-metals: foils, laminates and fabrics run at 10 mm/min; at 100 mm/min a viscoelastic adhesive reads higher and may change failure mode.

  • Unsupported heavy tails at low force: 200 mm of 0.7 mm aluminium weighs about 10 g, and a swinging tail adds oscillation to a 20 N trace; use the tail support and say so.

ISO 11339 vs ASTM D1876, ISO 8510-2 and ASTM D903

The ISO and ASTM T-peel methods are the same idea with different numbers, and the numbers are different enough that results are not interchangeable: the rate alone differs by 2.5×.

  • ISO 11339:2022: 25 mm strips from a 150 × 200 mm panel, bonded length ≥ 150 mm, 50 mm legs, preferred adherends 0.5 mm steel or 0.7/0.5 mm aluminium, crosshead 100 mm/min for metals (10 mm/min others), peel ≥ 150 mm, evaluate ~100 mm discarding 25 mm at each end, best-straight-line average with max and min, ≥ 5 specimens, ISO 291 conditioning, result in N/100 mm, ISO 10365 failure codes.

  • ASTM D1876: 152 × 305 mm panel bonded over 241 mm with 76 mm unbonded, 25 mm strips, reference adherend 0.81 mm clad 2024-T3 aluminium, crosshead 254 mm/min (127 mm/min peel), average over at least 127 mm of peel after the initial peak, ≥ 10 specimens, conditioning 7 days at 23 ± 1 °C and 50 ± 2 % RH, result in N/mm (lbf/in), failure reported as percent cohesive.

  • ISO 8510-2: 180° peel of a flexible adherend bonded to a rigid one, 100 mm/min, result in N per unit width with the ISO 6133 trace analysis; the flexible-to-rigid counterpart of this test.

  • ASTM D903: 180° stripping of a flexible adherend from a rigid one at 152 mm/min, 25 mm wide, result in N/mm; see our ASTM D903 guide.

  • ASTM F88 and ISO 11607 seal tests: peel of flexible packaging seals at 200 to 300 mm/min with supported or unsupported tails, for medical packaging rather than structural adhesives.

A lab asked for 'T-peel to ISO and ASTM' needs two specimen sets, two rates and two evaluation windows; the only shared hardware is the pair of 25 mm grips and the tail support.

Equipment: T-Peel Fixture, Grips and Machines for ISO 11339

Universal Grip's ISO 11339 T-peel fixture is a matched pair of pneumatic side-acting grips with a guided tail-support frame between them. The grips give equal, repeatable clamping on both legs from one air supply, the narrow jaws suit 25 mm wide strips, flat or serrated faces are fitted to suit the adherend, and the tail-support frame holds the bonded section for supported peel or is swung clear for unsupported peel. Capacity is 500 N standard with other capacities on request, construction is aluminium and stainless steel, the connection is a clevis or threaded adapter to suit the frame, and it mounts on electromechanical universal testing machines and low-force frames; specify specimen width and material, supported or unsupported peel, air supply and machine connection when ordering (part ref. UGC-ISO11339-PF).

  • Grips: the fixture's matched pneumatic grips keep clamping force constant through three minutes of peel; for occasional tests a pair of screw vise grips with 25 mm faces works but needs careful equal tightening.

  • Capacity math: flexible-to-flexible T-peel forces run from 2 to 40 N on 25 mm foils and laminates to about 50 to 150 N on structural epoxy between 0.5 mm steel legs (200 to 600 N/100 mm); a 500 N fixture and a 500 N or 1 kN load cell cover the range with the rupture force well inside 10 to 80 % of range.

  • Machines: a 2.5 kN benchtop universal testing machine with 500 mm or more of crosshead travel, or a Mark-10 tensile tester for QC, both at 100 mm/min with data logged at 100 Hz or faster.

  • Other peel geometries: 90°, 180°, floating-roller and climbing-drum fixtures are on the peel fixtures page, with the method overview on the peel testing application page and in our guide to peel test fixtures.

  • Related standards we equip: ASTM D1876 for the inch-based T-peel, ASTM D903 for 180° stripping, ISO 4587 for lap shear of the same adhesives on rigid adherends, the adhesives testing page and the full ISO standards hub.

Report Checklist

The ISO 11339 report contains: reference to ISO 11339:2022; the adhesive (type, source, code, batch, form); the adherends (material, thickness, width, surface preparation per ISO 17212); the bonding process (method, drying or pre-cure, cure time, temperature and pressure); the average adhesive thickness; the specimens (dimensions, construction, cutting method, number of panels, number tested, edge specimens identified); the conditioning atmosphere; the crosshead rate; whether the peel was supported or unsupported and which leg was in the moving grip; the averaging method; the average, maximum and minimum force in N and the peel resistance in N/100 mm for each specimen; the ISO 10365 failure type; and any deviation from the method.

ISO 11339 FAQ

What is ISO 11339?

ISO 11339 is the international T-peel test for adhesive bonds between two flexible adherends. Two thin strips, typically 0.5 mm steel or 0.7 mm aluminium, bonded over 150 mm are pulled apart by their 50 mm unbonded legs at 100 mm/min and the average peel force per width is reported as peel resistance in N per 100 mm. The current edition is ISO 11339:2022.

What are the ISO 11339 specimen dimensions?

Strips 25 mm wide and about 200 mm long with a bonded length of at least 150 mm and 50 mm unbonded legs at one end, cut as six strips from a 150 × 200 mm panel with the two edge strips reported separately. Preferred adherends are 0.5 ± 0.02 mm steel or 0.7 or 0.5 ± 0.02 mm aluminium.

What speed does ISO 11339 use?

A constant crosshead rate of 100 mm/min for metal adherends and 10 mm/min for other adherends. Because both legs move, the peel front advances at half the crosshead speed, 50 mm/min, and peeling 150 mm of bond takes about 300 mm of crosshead travel, three minutes at 100 mm/min.

How is the peel force evaluated in ISO 11339?

The test runs until at least 150 mm of bond has separated; the first 25 mm and the last 25 mm of peel are disregarded and a best straight line is drawn through the trace over about 100 mm of peel in the middle to give the average force, with the maximum and minimum also read. On the chart those are 50, 200 and 50 mm of crosshead travel.

What units does ISO 11339 report?

Peel resistance in newtons per 100 mm of width since the 2010 edition; the 2003 edition used kN/m. A 42 N average on a 25 mm strip is 168 N/100 mm, which equals 1.68 N/mm, 42 N/25 mm, 1.68 kN/m or 9.6 lbf/in; 1 N/mm = 100 N/100 mm = 5.71 lbf/in.

What is the difference between ISO 11339 and ASTM D1876?

D1876 uses a 152 × 305 mm panel with 241 mm bonded, 0.81 mm 2024-T3 aluminium, 254 mm/min crosshead (127 mm/min peel), averages over at least 127 mm after the initial peak, needs 10 specimens and reports N/mm; ISO 11339 uses a 150 mm bond, 0.5 mm steel or 0.7 mm aluminium, 100 mm/min, a 100 mm window with 25 mm discarded at each end, 5 specimens and N/100 mm. Results are not interchangeable.

How many specimens does ISO 11339 require?

Not fewer than five, with edge specimens from a panel reported separately. ASTM D1876 requires at least ten.

Which leg goes in the moving grip?

Each grip holds the outer 25 mm of one unbonded leg with equal clamping and square alignment. Where the adherends differ in flexibility, the standard's established instruction is to clamp the less flexible adherend in the moveable grip; record which way the specimen was mounted because it affects the trace.

What is supported versus unsupported T-peel?

In unsupported peel the bonded section hangs free between the grips and its weight and swing add to the force at low loads; in supported peel a guided frame holds the bonded section. The choice must be reported, and tail support is the usual choice for long metal strips at forces below about 50 N.

How are failure modes reported?

With ISO 10365 codes along the peeled length: cohesive (adhesive on both faces), adhesive (one face bare), special cohesive (thin film on one face), delamination and mixed modes as percentages. Only cohesive failures characterise the adhesive; adhesive failures point to surface preparation per ISO 17212.

Does ISO 11339 use ISO 6133 for averaging?

No. ISO 11339's own rule is a best straight line through the trace over the 100 mm window; ISO 6133 peak analysis is used by the tape and tear standards and may be added as a declared, separate analysis for stick-slip traces.

What fixture and machine are needed for ISO 11339?

A matched pair of 25 mm pneumatic grips with equal clamping, a tail-support frame, a 500 N fixture and a 500 N to 1 kN load cell, on a frame with 100 mm/min speed, at least 500 mm of crosshead travel and 100 Hz data logging; a 2.5 kN benchtop universal testing machine or a Mark-10 tester covers it. Typical forces are 2 to 40 N for foils and laminates and 50 to 150 N for structural epoxy on 0.5 mm steel.

Need a T-peel fixture, pneumatic grips or a complete low-force system for ISO 11339? Contact Universal Grip with your adherend material and thickness, expected peel force and machine connection and we will quote the right setup.

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