Tensile Testing Methods for Packaging Materials: Standards, Procedures, and Applications

Tensile testing is one of the most fundamental mechanical evaluation methods for packaging materials, quantifying tensile strength, elongation at break, and elastic modulus for plastic films, laminates, papers, foils, and heat seals. This technical guide explains the applicable ISO, ASTM, EN, JIS, and GB standards, along with sample preparation, test procedures, and data interpretation commonly used by packaging manufacturers and accredited third-party laboratories worldwide.

Technical Overview

Tensile testing, also known as tension testing, measures the force required to stretch a packaging material to yield or breakage and the extent to which the material elongates before failure. A specimen of defined geometry is clamped between two grips on a universal testing machine (UTM) and pulled at a constant crosshead speed while a load cell records force and displacement sensors or extensometers record elongation. The resulting force–elongation curve is used to derive tensile strength, elongation at break, elastic modulus, and other mechanical parameters.

For packaging, these properties are critical performance indicators. They determine whether a film can survive converting, printing, bag making, filling, sealing, transportation, and end use without splitting, necking, or losing package integrity. Because packaging materials range from micron-scale barrier films to heavy woven sacks, standards organizations such as ISO, ASTM International, CEN, JIS, and the Chinese GB system have established material-specific test methods, and selecting the correct standard, specimen geometry, and test speed is essential for reproducible, comparable results.

Testing Samples

Plastic Films and Sheets

Monolayer and coextruded films such as PE, PP (cast and oriented), PET, PA, PVC, EVOH, and cellophane are the most commonly tested packaging materials. Thin sheeting up to approximately 0.25 mm in thickness is typically tested as rectangular strip specimens in accordance with ASTM D882, ISO 527-3, or GB/T 13022. Thicker sheets are tested as die-cut dumbbell specimens under ASTM D638 or ISO 527-2.

Laminated and Composite Films

Multilayer structures such as PET/AL/PE, PET/PE, NY/PE, and paper/foil/polymer laminates are tested as complete assemblies so that the measured tensile response reflects the combined structure. Any interlayer delamination observed during testing should be noted, since it signals adhesion problems that may require separate peel evaluation.

Paper and Paperboard

Kraft sack paper, wrapping paper, carton board, and specialty papers are tested under ISO 1924-2, TAPPI T 494, ASTM D828, or GB/T 12914. Results are typically expressed as breaking force per unit width (kN/m) or as breaking length, which allows comparison between papers of different grammages.

Aluminum Foil and Foil Laminates

Blister lidding foils, cold-form foils, and foil sealants exhibit low elongation and low breaking forces. They require low-capacity load cells, gentle clamping pressure, and edge-defect-free specimens to obtain valid results.

Heat Seals and Seal Areas

Fin seals, lap seals, and perimeter seals from pouches, sachets, and blister packs are evaluated for seal strength using tension-type peel configurations described in ASTM F88 and JIS Z 0238. Seal strength data validate sealing process parameters such as temperature, dwell time, and pressure.

Nonwovens, Tapes, and Woven Fabrics

Nonwoven packaging, adhesive tapes, and woven polypropylene sack fabrics are tested using strip methods adapted from textile standards such as ASTM D5035, often with wider specimens and higher-capacity grips to accommodate their structure.

Testing Items

Depending on the material and the governing standard, tensile testing of packaging materials typically reports the following parameters:

• Maximum tensile force (N) and tensile strength (MPa), calculated as the peak force divided by the original cross-sectional area.
• Tensile stress at yield (MPa), identifying the onset of permanent deformation.
• Elongation at break (%) and elongation at yield (%), indicating ductility and formability.
• Elastic modulus (Young's modulus or secant modulus, MPa), characterizing stiffness.
• Breaking strength per unit width (N/mm or kN/m), the conventional expression for papers and boards.
• Seal strength (N per 25 mm of seal width), evaluated for heat-sealed joints.
• Energy to break or toughness (J), derived from the area under the force–elongation curve.
• Directional comparison (machine direction versus transverse direction) to quantify anisotropy.

Testing Methods

Applicable Standards

• ISO 527-1 and ISO 527-3: tensile properties of plastics, including film and sheeting strip specimens.
• ASTM D882: tensile properties of thin plastic sheeting up to 0.25 mm thickness.
• ASTM D638 and ISO 527-2: tensile properties of molded or die-cut plastic dumbbell specimens.
• ISO 1924-2, TAPPI T 494, ASTM D828, and GB/T 12914: tensile strength of paper and board.
• ASTM F88 and JIS Z 0238: seal strength of flexible barrier materials.
• GB/T 1040.3 and GB/T 13022: Chinese national standards corresponding to plastic film tensile testing.
• ISO 291, ASTM D618, and ISO 187: conditioning atmospheres for plastics and paper.

Specimen Preparation and Conditioning

Specimens are cut or die-stamped with smooth, defect-free edges, since nicks and burrs cause premature failure. Film strips are typically 15 mm or 25.4 mm wide; paper strips are typically 15 mm wide; thicker plastics use standardized dumbbell geometries. Thickness is measured at multiple points using a calibrated micrometer per ISO 4593 or ASTM D6988, and width is verified to calculate the cross-sectional area. Specimens are conditioned to equilibrium in a standard atmosphere, commonly 23 °C and 50% relative humidity, for the period defined by the applicable standard. Because films and papers are anisotropic, specimens are prepared and tested separately in both the machine direction (MD) and the transverse direction (TD), with at least five valid specimens per direction.

Equipment and Test Setup

A universal testing machine fitted with an appropriately sized load cell, commonly 50 N to 5 kN depending on the material, is used. Force verification is performed in accordance with ISO 7500-1 or ASTM E4, and extensometers are verified per ISO 9513 or ASTM E83. Pneumatic or mechanical side-action grips with rubber-faced or serrated inserts are preferred for films to prevent slippage without initiating breaks at the jaw faces. For modulus measurement, a contact or non-contact extensometer is recommended because crosshead displacement alone includes machine and grip compliance.

Test Procedure

• Verify instrument calibration, grip condition, and environmental settings before testing.
• Set the initial grip separation (gauge length) per the standard, for example approximately 50 mm for dumbbell specimens, 100 mm for film strips, and 100–180 mm spans for paper, as specified.
• Select the crosshead speed defined by the method, commonly 50 mm/min for rigid plastic dumbbells, 100–300 mm/min for films, about 20 mm/min rates of elongation for paper, and 200 mm/min for seal strength tests.
• Mount the specimen squarely in the grips with a small preload to remove slack, ensuring axial alignment to avoid bending or shear components.
• Run the test to break while recording the force–elongation curve at an adequate sampling rate.
• Repeat for the required number of specimens in each direction; specimens that fail at or in the grips are treated according to the standard's validity criteria and retested if necessary.

Data Processing and Reporting

Tensile strength is calculated as the maximum force divided by the original cross-sectional area, and elongation at break as the extension at break divided by the initial gauge length, expressed as a percentage. Modulus is determined from the initial linear region, for example as a secant modulus between defined strain limits in ISO 527-1 or as the 2% secant modulus in ASTM D882. The test report should identify the standard used, material and thickness, conditioning, specimen geometry, direction, test speed, individual values, mean, and standard deviation, together with any anomalous failures or delamination events. Results are compared against material specifications, control charts, or customer requirements.

Applications

Tensile testing data support nearly every stage of the packaging life cycle, from material development to end-use performance verification:

• Incoming inspection and roll release testing of films, papers, and foils at converting plants.
• Quality control of heat-sealing processes through routine seal strength verification.
• Material qualification, supplier comparison, and substitution studies, including downgauging and recyclable mono-material designs.
• Regulatory and customer compliance packages for food, pharmaceutical, and medical device packaging, often supported by data from accredited third-party laboratories operating under ISO/IEC 17025 quality systems.
• Shelf-life and aging studies, comparing retained tensile properties after accelerated aging, sterilization, or temperature cycling.
• Failure analysis of splitting films, weak seals, or packaging damaged during filling, handling, and distribution.

FAQ

Which tensile standard should be used for plastic packaging film?

ASTM D882, ISO 527-3, and GB/T 13022 are the principal methods for thin films, and they are broadly similar in principle but differ in specimen dimensions and test speeds. The choice should follow the specification agreed with the customer or regulator, and the exact method used must always be stated in the report.

Why do machine direction and transverse direction results differ?

Film orientation during blown or cast extrusion and fiber alignment during papermaking create anisotropy. Biaxially oriented films may show high strength in both directions, while uniaxially oriented materials can differ by a large factor, so both directions must be tested and reported separately.

How many specimens are required?

Most plastic film standards require a minimum of five valid specimens per direction, while paper standards typically require ten per direction. Specimens that fail at the grips are evaluated against the standard's validity criteria and retested when rejected.

What causes specimens to break at the grips, and how is it prevented?

Stress concentration from excessive clamping pressure, serrated jaw faces, or misalignment can cause jaw breaks. Remedies include reduced clamping pressure, rubber-faced grip inserts, improved specimen alignment, and careful edge preparation. Results from jaw breaks should be flagged or discarded per the standard.

How is seal strength different from tensile strength?

Tensile strength characterizes the bulk material, whereas seal strength, measured per ASTM F88, characterizes the performance of the sealed joint by peeling a 25 mm wide strip in a controlled tension configuration. Both are needed to fully assess pouch and sachet reliability.

Can tensile testing be performed under special environmental conditions?

Yes. Environmental chambers allow testing at sub-zero temperatures for cold-chain packaging, elevated temperatures for retort and hot-fill applications, and controlled humidity for paper and biopolymer materials, providing data that reflect real-world service conditions.