TPU Film Tensile Test: Strength and Elongation

A TPU film tensile strength test method measures the force needed to stretch a film strip and converts it to stress using the initial cross-sectional area. For thin films, agree on ASTM D882 or ISO 527-3, determine the test direction, measure the specimen and record the force and extension through rupture.

A thickness entry can adjust the reported strength even when the testing machine records exactly the same pull. That matters when a buyer is deciding whether to reject a roll, approve a substitute grade or pay for another laboratory test. Always consider the specimen and the test conditions prior to discussing results.

TPU film tensile test: what the numbers mean

Force describes how hard the machine pulls. Stress is the ratio of the force to the cross-sectional area of the specimen. Elongation describes extension relative to the initial length. The material testing report presents the stress-strain curve and defines the measurements of strength and elongation.

At the same stress and thickness, the wider specimen carries more tensile load because more material spans the grips. Dividing by the initial specimen width multiplied by film thickness gives nominal engineering stress, expressed in MPa when force is in N (Newtons) and area is in mm².

• Ultimate tensile strength: the maximum nominal stress reached during the pull.
• Stress at break: the stress calculated from the force at rupture. A specimen can reach its maximum force earlier.
• Elongation at break: the increase in measured length at rupture, divided by its initial gauge length.
• Tensile modulus: a stiffness measure obtained from the relevant part of the stress-strain response. These physical properties answer different design questions.

The British Plastics Federation’s test method guide categorizes load cells, which measure force, as different from extensometers, which measure strain. For packaging films, coefficient of friction is a separate handling measurement, which is listed separately by the BPF guide from tensile testing. A cited yield strength or yield stress requires a defined yield point or calculation rule; the curve may not present the same distinct features as a rigid plastic undergoing plastic deformation. In such cases, one can refer to the TPU film specification sheet for definitions.

ASTM D882 or ISO 527-3: choose the reporting basis

ASTM D882-26a, the current ASTM D882 standard, covers plastic thin sheeting and films less than 1.0 mm thick. ISO 527-3 is for tensile properties of plastic films and sheets of the same thickness range. These international standards provide a reporting basis. It is recommended to use the specified method and basis for the material supplied and the buyer’s intended end use, then adhere to that reporting basis for all laboratories.

ASTM’s current wording calls its method technically similar to ISO 527-3. Both address tensile properties of thin plastic materials; comparable results require aligned specimen preparation and testing procedures as well as the standard number. A purchase specification that named one method should not receive an unexplained result from the other.

For free-standing TPU films under 1.0 mm, ASTM D882 or ISO 527-3 is a suitable starting point for negotiating a thin-film test. TPU is also a thermoplastic elastomer, covered by ASTM D412. If a supplier or customer specifies D412, obtain agreement before using either thin-film method as a substitute. A molded test piece and converted film have different geometries and histories of processing.

D882 recognizes thin materials containing inseparable layers, laminations or coatings. By contrast, ISO 527-3:2018 states that it is not normally suitable for plastics reinforced by textile fibres. Determine whether the specimen is free TPU film, an inseparable multi-layer film or a textile laminate prior to deciding on the standard test method. When ordering TPU film for coated and laminated fabrics, distinguish the supplied film from the finished fabric assembly in the test brief.

Specimen preparation: thickness, edges and MD/TD

Edge quality affects where failure starts in the specimen. Conditioning belongs in the mechanical testing record because temperature, humidity and prior exposure may affect the measured mechanical response.

Instron’s D882 application guide, which links to the D882-18 edition, describes strips 5.0–25.4 mm wide and at least 50 mm longer than the initial grip separation. These dimensions provide a practical starting point for sample planning, and the laboratory’s test order should state the geometry adopted under its specified edition.

1. Identify the sample. Record grade, batch, roll location and whether a removable carrier is present.
2. Mark the directions. Label the machine direction before cutting, then identify the perpendicular transverse direction.
3. Prepare and inspect strips. Use the selected method’s dimensions and reject damaged preparation pieces before testing.
4. Condition and measure. Follow the agreed procedure, record the environment and measure each specimen using an appropriate thickness method.

Should plastic film be tested in MD and TD directions?

Yes. When you need to assess direction-dependent film behavior, test machine direction and transverse direction separately. In this context, MD is the film’s manufacturing travel direction; TD is across the film. Cutting direction should be recorded with each test result rather than lost by pooling all the results into a single average.

Manufacturing processes like extrusion can produce polymer films with different mechanical behavior along and across the web. For a flexible packaging converter pulling film across its width, an MD-only report leaves the relevant direction undetermined. Stipulate both directions in the test order and compare like directions between suppliers.

ASTM D618 explains why temperature and relative humidity must be standardized preceding and during the test. Document conditioning duration and test atmosphere together. Reproducible conditioning and full equilibrium with moisture are different objectives; choose the procedure required by the material specification.

For textured material, the thickness measurement needs particular attention: ISO 4593’s mechanical scanning method is unsuitable for embossed film or sheeting. Raised features can make a simple thickness reading a poor description of the cross-section carrying the load.

Testing machine setup: grips, load cell and test speed

A film test requires a testing system that holds the strip without slip or damage, resolves the expected force and measures extension over the required travel. The testing equipment should match the material properties and expected deformation. A large frame capacity doesn’t always indicate that a low force measurement is of good quality.

Can a universal testing machine test plastic film?

Yes, a universal testing machine can test plastic film if it has appropriate grips, a calibrated force range, and an extension measurement system calibrated for the test. The BPF equipment guide states these items individually since each is critical to the measurement.

Grip faces have to make sufficient contact to hold a thin film and not cut or crush the material at the edge. For very extensible materials check that the travel is sufficient to reach the expected break point. Optical measurement can track marks on the specimen; crosshead displacement describes machine movement and can include slip or deformation outside the intended measurement length.

Calculate crosshead speed in mm/min by multiplying the initial grip separation in mm by the selected initial strain rate in min⁻¹. Crosshead speed is determined by other factors such as the expected elongation at break. TPU is viscoelastic: control the loading conditions when evaluating the tensile properties instead of treating speed as a machine convenience setting.

• Keep the load-cell identification and valid verification range with the report.
• Record initial grip separation separately from a marked gauge length.
• State how slack or preload was handled.
• Retain the extension channel used for modulus and elongation calculations.

Tensile strength calculation: a thickness error example

The Thickness Bias Check calculates stress from force and corrects a nominal stress calculation using the original cross-sectional area. It separates a denominator error from a change in material quality. ASTM D882 controls specimen thickness among the other variables that must be controlled for accurate comparison.

A thickness error changes the cross-sectional area used to calculate tensile stress. For this hypothetical calculation, the strip is 10 mm wide and has a measured initial thickness of 0.10 mm. Its maximum force is 25 N, and its force at rupture is 20 N. Its initial marked gauge length is 50 mm, and the marks are 200 mm apart at break. These calculation inputs describe a worked example, not a TengYang test result or a prescribed specimen recipe. Biopdi illustrates the thickness effect: a 2.5 µm thickness error on a 50 µm film changes the calculated cross-sectional area by 5%, affecting calculated stress.

When a report looks unexpectedly strong, inspect the dimensions entered in the software before changing the film grade. If the original measured thickness and force data are available, the laboratory can correct a calculation entry and issue a corrected report. If the initial dimensions were never measured reliably, another tensile test with properly prepared specimens may be needed.

The table identifies maximum stress and stress at failure. Reporting only “strength” of a specimen can be misleading.

Test failures: distinguish tearing, slip and valid breaks

A low result needs a failure description before it becomes a material rejection. Edge-initiated tearing, movement in the grips, and a normal break describe different test events. ASTM D882 states that tearing failures give anomalous data that cannot be compared with normal failure, so retain observations alongside the curve.

“Defects in the edges will cause premature failures at the site of the defect and lower force and elongation values.”

A suspect specimen should be traceable in the test record. The reason for its exclusion/repetition should also be recorded, and the rules of the method selected should be followed; deleting the lowest values because they’re inconvenient biases the result. For a production problem, a sample of the supplied roll should be retained to distinguish a preparation fault from damage already present in the film.

Compare laboratory results before accepting a film

Reports should be compared field by field before ranking suppliers in MPa. A useful comparison should keep specimen construction, direction, conditioning and test setup consistent; ASTM D882’s comparison guide identifies several of these variables, and ASTM D618 covers the environmental conditions.

Consider two reports delivered to purchasing: one tests free film along the web; the other tests a film-and-carrier assembly across it. Their strength values evaluate different things. The table gives a route to a comparable result without automatically ordering a complete repeat program.

TengYang provides TPU film for reflective materials in both carrier and no-carrier options. Identify the specimen construction on the sample order. For TPU film for bonded apparel, assess the bonded assembly’s adhesion and durability as well as the film’s tensile response; the substrate and bonding process determine a separate part of performance.

Quality control can approve the test basis, and purchasing can compare equal scopes. The plant can trial the selected grade. Send the application and the required report fields with a custom TPU film sourcing request, so the sample and production specifications describe the same material.

Testing cost and sample quantity

KMUTNB’s Industrial Chemistry department posts a rate of 500 Thai baht per sample for its universal testing service, which lists ASTM D638 and ASTM D882. This is one university’s service rate. A commercial project quote must specify the directions, valid replicates and preparation work included.

Count test conditions first, then count pieces. If your plan calls for two directions with five valid specimens in each, that’s a total of ten pulls per condition. Additional aging conditions create additional groups. In this worked example using 10 mm-wide strips with 50 mm initial grip separation, an additional 50 mm gives a 100 mm strip length. Ten strips therefore require 10,000 mm² of cut specimens before allowing for cutting waste, setup pieces or repeats. This is a cut-piece calculation; supply enough material to cut both MD and TD strips of the agreed length.

Supply extra material for cutting losses, setup tests and justified repeats. DDL’s laboratory guidance states exploratory tests may be necessary to identify suitable settings. A request for modulus may also alter specimen preparation and measurement, so include it before the laboratory quotes.

• Define whether the fee covers raw sample preparation or supplied cut strips.
• Separate each direction and conditioning state in the scope.
• List the required properties and individual results, curves and summary statistics.
• State the report purpose, delivery date and treatment of abnormal failures.

Finance gets a clearer comparison from an itemized scope than from the lowest per sample rate. A less expensive quote, which omits needed direction, can leave the purchasing decision unresolved.

Laboratories that test thin plastic films

Intertek and Touchstone Research Laboratory describe film tensile testing services, while KMUTNB lists D882 among its universal testing methods. Choose the receiving lab based on the specimen, measurement range and purpose of the report. Equipment vendors sell tensile testing machines, while a contract lab performs the test and provides the agreed report.

When a customer needs an accredited report, match the requested test to the laboratory’s current accreditation scope and receiving site. Retain the accepted scope with the purchase order. For internal development, the required report may be a documented comparison under a mutually agreed procedure.

ASTM D882-26a: keep the edition with the result

ASTM lists D882-26a as active, updated October 1, 2026. An edition identifier belongs with the tensile test method on the report. ISO identifies ISO 527-3:2018 as current after its 2024 confirmation, so the year in a standard designation is not itself a sign that it is obsolete.

When adopting a revised edition of the standard, review the changed requirements with the laboratory and evaluate if a comparison run is necessary. Retain the original reports to check whether a later shift in results would indicate a change in the material and the test method used.

For the next sample request, pair your application with the appropriate TengYang TPU film options and attach the agreed test brief. Include grade, construction and roll direction so the laboratory can test the material you wish to purchase.

Frequently asked questions