ISO 527-3
Tensile Properties of Plastic Films and Sheets

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

ISO 527-3 is the international standard for the tensile properties of plastic films and sheets less than 1 mm thick. It sits under the general principles of ISO 527-1 and defines the specimens, grip separations, gauge lengths and test speeds for packaging film, battery separator film, agricultural film, laminates, labels, release liners and thin extruded sheet. From it come the tensile strength, strain at break, nominal strain, stress at yield and tensile modulus that film data sheets quote, in both the machine direction (MD) and the transverse direction (TD).

This guide covers the current edition and its history; the scope and the 1 mm thickness line that separates it from ISO 527-2; the Type 2 strip and the Type 4 and Type 5 dumb-bells with their dimensions, gauge lengths and grip distances; the speed list with strain-rate arithmetic; the 0.05 to 0.25 % chord modulus and why ISO 527-3 insists on an extensometer or gauge marks where ASTM D882 tolerates crosshead travel; cutting, measuring and conditioning; the step-by-step procedure; the calculations with a worked example; the common errors and how large they are; a numeric comparison with ASTM D882; and the grips, cutters, extensometers and machines Universal Grip supplies for film testing. The plastics page gives the lab overview and the ISO standards hub lists every ISO method we equip.

In this guide: What ISO 527-3 Covers and Its Current Edition · Specimen Types: 2, 4 and 5 · Cutting, Measuring and Conditioning Film Specimens · Test Speeds and Strain Rates · Tensile Modulus and Strain Measurement · Grips and Alignment for Film · Step-by-Step ISO 527-3 Procedure · Calculations and a Worked Example · Common Errors and How Large They Are · ISO 527-3 vs ASTM D882 · Equipment for ISO 527-3 Film Testing · FAQ

What ISO 527-3 Covers and Its Current Edition

ISO 527-3 applies to plastic films and sheets of thickness below 1 mm. Thicker sheet is tested to ISO 527-2 with the A1 or A2 dumb-bell; textile-reinforced coated fabrics go to ISO 1421, fibre-reinforced laminates to ISO 527-4 and cellular materials to ISO 1798. The standard covers every property defined in ISO 527-1: tensile strength and the stress at break, strain at break, nominal strain, yield stress and yield strain, stress at a chosen strain, and tensile modulus. Films that yield and draw, such as polyethylene and polypropylene, use the nominal-strain route of ISO 527-1 Method B after the yield point, because an extensometer cannot follow a neck that forms at a random position and then travels along the strip.

The current edition is ISO 527-3:2018, the second edition. It merged the 1995 text with its two corrigenda, updated the references to ISO 527-1 and swapped two clauses; the specimens and speeds did not change. ISO confirmed it at the 2024 systematic review. EN, BS EN and DIN EN ISO 527-3 and GB/T 1040.3 are identical adoptions; JIS K 7127 is a modified one.

ISO 527-3 borrows its apparatus, calculation and report clauses from ISO 527-1; the sections below merge the two parts so that a lab can run the test from this page alone.

Specimen Types: 2, 4 and 5

ISO 527-3 defines three specimen types of its own. Type 2 is the preferred one and is the one almost every film test uses; Types 4 and 5 are dumb-bells for materials that cannot be tested as a plain strip. All three keep the film's as-made thickness; nothing is machined. Dimensions are in millimetres.

• Type 2, parallel strip (preferred): width 10 to 25 mm, overall length at least 150 mm, initial distance between grips 100 mm, gauge length 50 mm. 15 mm is the usual width; 25 mm suits soft or very thin films where a wider strip gives a measurable force. Width must be uniform and the edges clean.

• Type 4, dumb-bell: a shoulder-type specimen with a 10 mm wide parallel portion and a 50 mm gauge length, for films that repeatedly fail at or inside the grips when tested as strips. The shoulders move the failure into the parallel section. It is die-cut.

• Type 5, small dumb-bell: overall length at least 115 mm, end width 25 ± 1 mm, narrow width 6 ± 0.4 mm, narrow length 33 ± 2 mm, radii 14 ± 1 mm and 25 ± 2 mm, gauge length 25 mm, grip distance 80 mm. It is the same outline as the DIN 53504 S1 rubber die, so one die serves both. It suits highly extensible films, elastomer-like sheet and coated papers where a 150 mm strip would stretch past the crosshead travel.

Start with a Type 2 strip: no stress concentration, cut in seconds with a two-blade cutter, largest gauge length. Move to Type 5 when a 100 mm grip distance runs out of travel on a very extensible film, and to Type 4 only when strips keep breaking at the jaw after faces and alignment have been checked. Test at least five specimens per direction and report the type, because strip and dumb-bell results are not interchangeable.

Some equipment literature lists a Type 1B specimen under ISO 527-3; that geometry belongs to ISO 527-2 and rigid sheet over 1 mm. For film the standard's own types are 2, 4 and 5.

Cutting, Measuring and Conditioning Film Specimens

Edge quality decides the result: a nick on the edge of a 20 µm strip becomes a tear starter and the specimen fails early with a strain at break that has nothing to do with the material. Strips are cut with a double-blade cutter that produces both edges in one stroke, or with a fresh razor blade against a straight edge; dumb-bells are die-cut with a sharp die in an arbor press or die press. Specimens with any visible defect are discarded. Cut and label sets in both the machine and transverse directions.

Thickness is measured to ISO 4593 with a dead-weight dial gauge of 0.001 mm resolution at several points along the gauge length, and the mean is used for the cross-section. Width is measured to ISO 16012 to 0.1 mm, or taken as the cutter blade spacing if the cutter is calibrated. Every stress value is force divided by width times thickness, so a 1 µm error on a 12 µm film is an 8 % error in strength and modulus; thickness, not force, is the dominant uncertainty in thin-film results.

Conditioning follows ISO 291 unless the material specification says otherwise: 23 ± 2 °C and 50 ± 10 % relative humidity, in practice for at least 16 hours, with the test run in the same atmosphere. Hygroscopic films such as polyamide and cellulose shift markedly with humidity, so the conditioning record is part of the result; hot and cold tests soak specimen and grips in an environmental chamber first.

Test Speeds and Strain Rates

ISO 527-3 takes its speeds from ISO 527-1 Table 1 and lets the material specification choose. In the absence of one, the modulus is measured at 1 mm/min and the other properties at one of 5, 50, 100, 200, 300 or 500 mm/min, chosen so that the specimen breaks in a reasonable time. Tolerances are ± 20 % on the slow speeds and ± 10 % on the fast ones. Because the Type 2 grip distance is 100 mm, converting to a nominal strain rate is easy:

• 1 mm/min on 100 mm: 1 %/min, the modulus speed. On the Type 5 grip distance of 80 mm it is 1.25 %/min.

• 5 mm/min: 5 %/min, used for stiff, brittle films such as cast polystyrene, PET at low strain or highly filled sheet.

• 50 and 100 mm/min: 50 to 100 %/min, the usual choice for PET, BOPP, BOPA and other oriented films that break between 50 and 200 % strain.

• 200 to 500 mm/min: 200 to 500 %/min, used for polyethylene, plasticised PVC, polyurethane and other films that draw to several hundred percent; at 500 mm/min a 400 % break takes less than a minute.

Modulus and strength can be run on separate specimens or as a two-speed test: 1 mm/min until the strain passes 0.3 %, then the strength speed. Report the speed used; the same film at 50 and at 500 mm/min gives different tensile strengths, and the numbers cannot be compared without it.

Tensile Modulus and Strain Measurement

The tensile modulus is the chord between 0.05 % and 0.25 % strain, or a linear regression over the same interval, measured on the 50 mm gauge length (25 mm for Type 5). On 50 mm those strains are 25 µm and 125 µm of extension, so the measuring device must resolve a few micrometres; that is why ISO 527-1 calls for an extensometer of ISO 9513 class 1 for modulus and why crosshead travel, which includes grip seating, load-train compliance and slip, cannot be used. This is the central difference from ASTM D882, which allows crosshead displacement on a long grip separation.

The device follows what the film can carry:

• Video extensometer: the default for thin film. Two ink marks or printed dots at 50 mm are tracked optically, nothing touches the specimen, the marks are followed to break and MD/TD sets need no re-rigging. Our video extensometers resolve well inside class 1 on a 50 mm field, and the Vector 3D extensometer adds width-change tracking for Poisson's ratio or necking studies.

• Clip-on extensometer: only on stiff sheet, roughly 100 µm and up, where the knife edges and arm mass will not kink or tear the film. Lightweight clip-on extensometers with low contact force work on PET and polycarbonate sheet; they must be removed before break on brittle sheet.

• Gauge marks and nominal strain: where no extensometer is fitted, the standard requires gauge marks at 50 mm applied with ink or wax, never scratched, and the strain at break is read from the marks. After the yield point of a drawing film, ISO 527-1 Method B takes the nominal strain from grip separation, since the neck leaves the gauge length.

Grips and Alignment for Film

ISO 527-1 requires that the specimen is held without slip or damage, with uniform pressure across the width, on the load axis. Film makes all three hard: it thins as it stretches, tears at any edge damage, and a 15 mm strip twisted by half a millimetre is already misaligned. Four grip types are in common use:

• Pneumatic grips: the first choice for most films. The clamping force is set by air pressure, stays constant as the film thins and is the same on every specimen. Flat rubber-faced jaws suit the general run of packaging films; line-contact faces, a round bar against a flat, concentrate the clamp on a single line and stop slip on slick films such as PTFE, silicone-coated liners and separator films. Face width should exceed the specimen width. Foot pedals leave both hands free to place the strip square.

• Roller grips: self-tightening eccentric rollers that grip harder as the load rises, with no air supply needed. They are the answer for very thin, slippery or very strong films that pull out of flat faces, and for strips that will see several hundred newtons.

• Vise grips: manual screw grips with rubber or smooth faces for occasional film testing on a Mark-10 force tester or a small frame. Clamping force depends on the operator, so they are kept for low-volume work.

• Wedge grips: not for film under about 0.3 mm; the wedge action crushes the jaw edge. They belong on ISO 527-2 sheet.

Alignment is set by the grip geometry: a specimen stop, centring edge or loading jig places every strip on the load axis. A preload of about 1 % of the expected strength, below 0.05 % strain, straightens the film before the modulus segment. Specimens that slip or fail at the jaw line are discarded and replaced; a run of jaw failures means the faces, pressure or edge cut needs attention, not that the film is weak. A mark drawn across the strip at the jaw line makes slip visible at a glance.

Step-by-Step ISO 527-3 Procedure

• 1. Condition the film to ISO 291 (23 ± 2 °C, 50 ± 10 % RH) or the material specification, and keep the testing room in the same atmosphere.

• 2. Cut at least five Type 2 strips, 15 mm or 25 mm wide and at least 150 mm long, in MD and five in TD with a two-blade strip cutter; or die-cut Type 5 or Type 4 dumb-bells. Inspect every edge and discard any with defects.

• 3. Measure thickness to ISO 4593 at several points along the gauge length and record the mean; measure or take the calibrated cutter width. Apply gauge marks at 50 mm (25 mm Type 5) if no extensometer is used.

• 4. Set the machine: a load cell matched to the expected force (a 100 N to 1 kN cell for most films), a grip distance of 100 mm (80 mm for Type 5), the grip pressure and faces for the film, and the speed or speeds.

• 5. Mount the strip square to the load axis, clamp the top grip, let the strip hang straight, clamp the bottom grip and apply the small preload.

• 6. Run at 1 mm/min for modulus until past 0.3 % strain, then at the strength speed to break, or run separate specimens for each. Record force and extensometer strain continuously; switch to nominal strain from grip separation after yield for drawing films.

• 7. Check the failure: a break at or within the jaw, or a specimen that slipped, is discarded and another tested in its place.

• 8. Calculate stress on the original cross-section, strain on the gauge length, the chord modulus between 0.05 and 0.25 %, and report mean, standard deviation and the number tested for each direction.

• 9. Report the standard part, film, thickness, direction, specimen type, cutter, grip type and faces, gauge length versus grip separation, speeds, strain method, conditioning and any rejected specimens.

Calculations and a Worked Example

All calculations come from ISO 527-1. With F the force in newtons, b the width and h the thickness in millimetres, L0 the gauge length and L the grip separation:

• Tensile stress: σ = F / (b × h), in MPa. Tensile strength σm is the first local maximum of stress; stress at break σb is the stress at fracture.

• Strain: ε = ΔL0 / L0 from the extensometer or gauge marks; nominal strain εt = ΔL / L from grip separation, used for strain at break after yield.

• Tensile modulus: Et = (σ2 − σ1) / (ε2 − ε1) with ε1 = 0.0005 and ε2 = 0.0025, or the slope of a least-squares line through the same interval.

• Stress at x % strain: read directly from the curve, for example σ at 2 % or 5 % for packaging specifications.

Worked example, a 12 µm PET film, Type 2 strip 15 mm wide. The mean thickness from five ISO 4593 readings is 0.0121 mm, so the cross-section is 15.0 × 0.0121 = 0.1815 mm². At 1 mm/min the force at 0.05 % strain is 0.73 N and at 0.25 % strain 4.35 N, giving σ1 = 0.73 / 0.1815 = 4.02 MPa and σ2 = 4.35 / 0.1815 = 23.97 MPa. The modulus is Et = (23.97 − 4.02) / (0.0025 − 0.0005) = 19.95 / 0.002 = 9,975 MPa, which rounds to 10.0 GPa, a normal value for biaxially oriented PET in the machine direction. The test then continues at 100 mm/min; the maximum force is 38.1 N, so σm = 38.1 / 0.1815 = 210 MPa, and the gauge marks are 50.0 mm apart at the start and 108.5 mm at break, so εb = (108.5 − 50.0) / 50.0 = 1.17, reported as 117 %. Had the thickness been read as 0.0130 mm, both values would have been reported 7 % low.

A drawing film: a 25 µm LLDPE strip 15 mm wide (0.375 mm²) reaches 7.1 N, so σm = 18.9 MPa; after yield the nominal strain comes from grip separation, and 380 mm of crosshead travel on the 100 mm grip distance gives a nominal strain at break of 380 %, which is why polyolefin film needs at least 500 mm of travel.

Common Errors and How Large They Are

• Using crosshead travel for modulus: on a 100 mm grip distance the apparent strain includes grip seating and film straightening; moduli read 20 to 50 % low and scatter widely. ISO 527-3 requires an extensometer or gauge marks for this reason.

• Thickness measured with the wrong instrument: a hand micrometer on a soft film compresses it; a 2 µm error on a 20 µm film shifts every stress value by 10 %. Use an ISO 4593 dead-weight gauge.

• Edge damage from a dull blade: ragged edges start tears and can halve the strain at break. Replace blades often.

• Jaw failures counted as valid: a break at the jaw line is a grip artefact and must be replaced; counting it lowers the mean and inflates the scatter.

• Slip in flat faces: slick films creep out of smooth faces as they thin and the curve shows a false yield plateau. Switch to line-contact faces or roller grips.

• Testing one direction only: oriented films differ two- to three-fold between MD and TD.

ISO 527-3 vs ASTM D882

ISO 527-3 and ASTM D882 test the same films, but ASTM itself notes they are similar and not technically equivalent:

• Specimens: ISO Type 2 strip 10 to 25 mm wide and at least 150 mm long, plus Type 4 and 5 dumb-bells; ASTM uses strips only, 5 to 25.4 mm wide, at least 50 mm longer than the grip separation, with a width-to-thickness ratio of at least 8.

• Grip separation and gauge length: ISO fixes 100 mm between grips with a 50 mm gauge length (80 and 25 mm for Type 5); ASTM uses 250 mm for modulus (100 mm permitted) and 125, 100 or 50 mm for break properties according to the expected elongation, with the gauge length equal to the grip separation.

• Strain: ISO requires an extensometer or gauge marks; ASTM allows crosshead displacement, with an extensometer optional.

• Speeds: ISO 1 mm/min for modulus and 5 to 500 mm/min for the rest; ASTM 25 mm/min for modulus on the 250 mm separation and 12.5, 50 or 500 mm/min according to elongation class.

• Modulus: ISO chord between 0.05 and 0.25 % strain; ASTM initial tangent after toe compensation, with a secant modulus optional.

• Count: ISO at least five per direction; ASTM at least five, or ten for anisotropic film, five in each direction.

• Extra outputs: ASTM reports breaking factor in N/m and tensile energy to break in MJ/m³; ISO reports nominal strain and stress at a chosen strain.

A lab serving both markets runs the same grips, cutter and video extensometer for both and keeps two methods in the software; results are reported under the standard that was run, never converted.

Equipment for ISO 527-3 Film Testing

A film tensile system means small forces, long travel, careful gripping and optical strain. A 25 µm LLDPE strip 15 mm wide breaks at about 7 N, a 12 µm PET strip at 35 to 40 N, a 50 µm BOPP strip at around 150 N and a 500 µm polycarbonate sheet 25 mm wide at about 800 N. Use a 100 N cell for thin polyolefin and polyester film and a 500 N or 1 kN cell for thicker films and sheet.

• Grips: pneumatic grips in the 1 kN class with flat rubber faces and line-contact faces, 25 mm or wider; roller grips for slick or very strong film; vise grips for low-volume work. Each is available with adapters for any testing machine.

• Machines: a single-column Mark-10 tensile tester or our 2.5 kN and 5 kN benchtop UTMs with at least 500 mm of crosshead travel cover films; the 10 kN benchtop adds the capacity for thick sheet and the ISO 527-2 dumb-bells on the same frame.

• Strain: a video extensometer tracking 50 mm gauge marks, non-contact to break, is the standard fit; the Vector 3D extensometer for Poisson's ratio and necking; a light clip-on extensometer for stiff sheet.

• Cutting: two-blade strip cutters for 10, 15 and 25 mm Type 2 strips, Type 5 (DIN S1) and Type 4 dies, and a die press that cuts a clean edge without dragging the film.

• Environment: an environmental chamber for hot and cold film tests, with the video extensometer reading through the window.

Related film tests on the same frame: puncture to ASTM F1306, friction to ASTM D1894, seal strength to ASTM F88 and tear to ISO 6383. See also ISO 527-1, ISO 527-2 and ASTM D882.

ISO 527-3 FAQ

What thickness does ISO 527-3 cover?

Films and sheets below 1 mm thick. Sheet of 1 mm and above is tested to ISO 527-2 with the A1 or A2 dumb-bell; coated fabrics go to ISO 1421 and fibre-reinforced laminates to ISO 527-4.

What is the ISO 527-3 Type 2 specimen?

A parallel strip 10 to 25 mm wide and at least 150 mm long, clamped with 100 mm between the grips and a 50 mm gauge length. It is the preferred specimen; 15 mm is the usual width and 25 mm is used for soft or very thin films.

What are ISO 527-3 Type 4 and Type 5 specimens?

Dumb-bells for films that fail in the grips or stretch too far as strips. Type 5 is 115 mm long with 25 mm ends, a 6 × 33 mm neck, a 25 mm gauge length and an 80 mm grip distance (the DIN 53504 S1 outline); Type 4 has a 10 mm neck and a 50 mm gauge length.

What test speed does ISO 527-3 use?

1 mm/min for the tensile modulus, and 5, 50, 100, 200, 300 or 500 mm/min for strength and elongation, chosen so the specimen breaks in a reasonable time, unless the material specification states a speed. On the 100 mm grip distance 1 mm/min is 1 %/min and 500 mm/min is 500 %/min.

How is tensile modulus calculated in ISO 527-3?

As the chord or regression slope between 0.05 % and 0.25 % strain, measured with an ISO 9513 class 1 extensometer or by optical tracking of 50 mm gauge marks. On a 50 mm gauge length that interval is 25 to 125 µm of extension, which crosshead displacement cannot resolve.

Do I need an extensometer for ISO 527-3?

The standard requires either an extensometer or gauge marks; crosshead travel alone is not accepted for strain. A video extensometer tracking ink marks is the usual choice for thin film because nothing touches the specimen; clip-on extensometers are used only on stiff sheet that can carry them.

How many specimens does ISO 527-3 require?

At least five per property, and five in each of the machine and transverse directions for anisotropic film. Specimens that slip or break in the grips are discarded and replaced.

What grips are used for plastic film tensile testing?

Pneumatic grips with flat rubber faces for general films and line-contact faces for slick films, self-tightening roller grips for very thin or very strong film, and manual vise grips for occasional work. Wedge grips crush film at the jaw edge and are kept for rigid sheet.

What is the difference between ISO 527-3 and ASTM D882?

Similar but not equivalent. ISO uses a 100 mm grip distance, a 50 mm gauge length and requires an extensometer or marks; ASTM uses 250 mm for modulus, 125, 100 or 50 mm for break properties and allows crosshead strain. ISO speeds are 1 and 5 to 500 mm/min; ASTM 25 mm/min for modulus and 12.5, 50 or 500 mm/min by elongation class. Modulus is a 0.05 to 0.25 % chord in ISO and an initial tangent in ASTM.

How is film thickness measured for ISO 527-3?

To ISO 4593, with a dead-weight dial gauge reading to 0.001 mm at several points along the gauge length, using the mean. A 1 µm error on a 12 µm film changes every stress value by about 8 %, so thickness is the largest uncertainty in film results.

What conditioning does ISO 527-3 specify?

ISO 291 standard atmosphere, 23 ± 2 °C and 50 ± 10 % relative humidity, for at least 16 hours in practice, with the test run in the same atmosphere unless the material specification says otherwise.

What load cell and machine capacity do I need for film?

About 7 N for 25 µm LLDPE, 35 to 40 N for 12 µm PET and around 800 N for 0.5 mm polycarbonate sheet on 15 to 25 mm strips; a 100 N to 1 kN load cell on a 2.5 or 5 kN benchtop frame or Mark-10 tester with 500 mm of travel covers almost all films.

Need pneumatic grips, roller grips, a strip cutter or a complete film tensile system for ISO 527-3? Contact Universal Grip with your film thickness, width and expected elongation and we will quote the right setup.