Packaging Material Breaking Force Testing: Standards, Methods, and Applications

Breaking force testing is one of the most fundamental mechanical evaluations for packaging materials, quantifying the maximum tensile load that films, foils, laminates, and paper-based structures can withstand before fracture. Reliable breaking force data ensures that packages survive filling, sealing, transportation, and end-use handling without failure. This article explains the principles, applicable standards, sample types, test procedures, and typical applications of tensile breaking force testing performed in accredited third-party laboratories.

Technical Overview

Breaking force, also known as tensile breaking force or ultimate tensile force, is the maximum force a packaging material sustains when it is stretched in a single direction until fracture occurs. During the test, a specimen of defined width and gauge length is clamped between the grips of a universal testing machine and pulled apart at a constant crosshead speed while force and elongation are continuously recorded. The highest force value reached on the force-elongation curve before rupture is reported as the breaking force, expressed in newtons (N) or newtons per unit width, such as N/15 mm for plastic films.

For packaging applications, breaking force is a critical quality attribute because it directly reflects the ability of a material to withstand the mechanical stresses of converting, filling, sealing, and distribution. Films and laminates are anisotropic: oriented films are typically stronger in the machine direction (MD) than in the transverse direction (TD), so testing in both directions is essential. In multilayer laminates, the measured breaking force reflects the combined contribution of every layer as well as the quality of the lamination itself, making it a sensitive indicator of adhesive bonding and extrusion coating consistency.

Testing is performed in accordance with internationally recognized standards, including ISO 527-1 and ISO 527-3 for plastic films and sheets, ASTM D882 for thin plastic sheeting, ASTM D638 for thicker plastic specimens, ISO 1924-2 and ASTM D828 for paper and paperboard, JIS K 7127 for plastic films supplied to the Japanese market, and GB/T 1040.3 and GB/T 12914 as Chinese national equivalents. Accredited third-party laboratories perform these tests using calibrated load cells, traceable measurement equipment, and documented procedures to ensure accurate, reproducible, and mutually recognized results.

Testing Samples

Plastic Monolayer Films

Single-layer films such as PE, CPP, BOPP, PET, PA, PVC, and EVOH-based structures, typically ranging from 20 to 200 micrometers in thickness, are tested as rectangular strips cut in both the machine and transverse directions. These materials form the inner sealing layers, outer print webs, and barrier layers of the majority of flexible packages.

Flexible Composite Laminates

Multilayer structures such as PET/AL/PE, BOPP/VMPET/CPP, PA/PE, and paper/foil/polyolefin laminates are tested to verify overall web strength and lamination integrity. Breaking force results confirm that the laminate can run reliably on form-fill-seal and pouch-making equipment without web breaks or delamination under tension.

Aluminum Foils and Foil Laminates

Hard aluminum blister foils, tropical blister laminates, and cold-formable foils are characterized by high strength but low elongation, which makes them sensitive to grip effects and specimen preparation quality. Testing these materials supports pharmaceutical packaging qualification and incoming material control.

Paper and Paperboard

Kraft paper for industrial sacks, coated and printed papers for labels and sachets, and paper-based laminates are tested using tensile testers operating at a constant rate of elongation in accordance with ISO 1924-2, ASTM D828, or GB/T 12914. Machine-direction strength is particularly important for web-fed converting operations.

Adhesive Tapes, Labels, and Strapping

Backing films for adhesive tapes, label facestocks, and plastic or paper strapping used for palletized goods are evaluated for breaking force to ensure the material will not snap under winding, dispensing, or load-securing tension.

Medical and Pharmaceutical Packaging Materials

Porous nonwoven lid materials, top web films for blister trays, and peelable lid stocks are tested for breaking force, which complements seal strength testing performed in accordance with ASTM F88 and provides a complete picture of package mechanical performance.

Testing Items

Depending on the material and the governing specification, a breaking force test campaign typically reports the following parameters for each test direction:

• Tensile breaking force (N or N/15 mm): the maximum force recorded at rupture
• Tensile strength (MPa): breaking force divided by the original cross-sectional area
• Elongation at break (%): extension at rupture relative to the initial gauge length
• Yield strength and elongation at yield, where a distinct yield point exists
• Tensile modulus, reported as Young's modulus or a defined secant modulus such as the 1% secant modulus for films
• Machine direction and transverse direction results for all reported parameters
• Related properties such as heat seal strength and seal breaking force per ASTM F88, where seal performance must be assessed alongside substrate strength

Testing Methods

Specimen Preparation

Specimens are die-cut or razor-cut from representative, defect-free regions of the material, well away from seals, folds, printed registration marks, and damaged edges. Plastic films are normally tested as rectangular strips of 15 mm or 25 mm width with an initial grip separation of 100 mm, while dumbbell-shaped specimens may be used for materials prone to grip breaks or when specified by standards such as ASTM D638. For paper and board, standard strip dimensions and gauge lengths defined in ISO 1924-2 or ASTM D828 apply. A minimum of five valid specimens per direction is required, and additional specimens are tested if any break occurs in or at the grips.

Conditioning

Prior to testing, specimens are conditioned in a standard laboratory atmosphere of 23 ± 2 °C and 50 ± 5% relative humidity in accordance with ISO 291 or ASTM D618, typically for a minimum of 24 hours for films and longer for paper-based materials conditioned per ISO 187. Conditioning is essential because temperature and moisture content measurably influence the tensile behavior of polymers and cellulose-based materials.

Equipment and Setup

A universal testing machine fitted with a calibrated load cell is used, with the cell capacity selected so that the expected breaking force falls within the accurately measured portion of the range, generally between 10% and 90% of full scale. Pneumatic or mechanical grips are fitted with appropriate faces, such as rubber-coated, serrated, or smooth inserts, sometimes combined with reinforcing tabs, to prevent slippage and premature grip breaks. Elongation is determined either by crosshead displacement or, where greater accuracy is required, by a contact or non-contact extensometer.

Test Procedure

• Measure specimen width and thickness at several positions and calculate the initial cross-sectional area
• Clamp the specimen centrally and squarely in the grips and apply a small preload to remove slack without stressing the material
• Select the crosshead speed specified by the governing standard, taking into account the expected elongation of the material, with higher speeds such as 500 mm/min used for highly extensible films and lower speeds for foils and papers
• Start the test and extend the specimen at constant speed until complete rupture, recording the full force-elongation curve
• Discard results from specimens that fail in or at the grips and test replacement specimens until the required number of valid results is obtained
• Calculate breaking force, tensile strength, and elongation at break, and report the mean, range, and standard deviation for each direction

Calculation of Results

The breaking force is read directly as the peak force on the recorded curve. Tensile strength is calculated as the breaking force divided by the original cross-sectional area, and elongation at break is calculated as the increase in gauge length at rupture divided by the initial gauge length, expressed as a percentage. For very thin films where thickness measurement uncertainty is significant, force per unit width is often the preferred reporting basis, as recognized in ISO 527-3 and ASTM D882.

Interpretation

Results are compared against internal specifications, customer requirements, or regulatory limits. The ratio between machine-direction and transverse-direction strength reveals the degree of molecular orientation, while lot-to-lot variation in breaking force can signal process drift in extrusion, orientation, coating weight, or lamination curing. A structured comparison of substrate breaking force with seal strength also helps determine whether package failures originate in the base material or in the sealing process.

Applications

Breaking force testing supports decision-making across the entire packaging life cycle, from material development to routine production control:

• Routine quality control of flexible packaging materials in the food, beverage, cosmetic, and pharmaceutical industries
• Incoming inspection and supplier qualification for purchased films, foils, laminates, and papers
• Development and optimization of new multilayer laminate structures and adhesive systems
• Stability and aging studies, including accelerated aging and retort processing, to track retention of mechanical properties over time
• Failure analysis of packages that split, tear, or fracture during filling, sealing, or distribution
• Technical documentation for regulatory submissions, customer specifications, and international market access, including EN, ISO, ASTM, JIS, and GB compliance programs

Because the test is fast, quantitative, and destructive only to small strips of material, it is one of the most cost-effective tools available for verifying that packaging materials consistently meet the mechanical demands of real-world supply chains.

FAQ

Question: What is the difference between breaking force and tensile strength?

Answer: Breaking force is the absolute maximum load, in newtons, that the specimen carries before it fractures, while tensile strength normalizes that force by the original cross-sectional area and is expressed in megapascals. Breaking force depends on specimen dimensions, whereas tensile strength allows comparison between materials of different thickness. For very thin films, force per unit width is frequently reported as the most reproducible parameter.

Question: Which standard should be used for my material?

Answer: Thin plastic films and laminates below approximately 1 mm are normally tested to ISO 527-3, ASTM D882, JIS K 7127, or GB/T 1040.3; thicker plastic sheets and rigid components to ISO 527-1 and 527-2 or ASTM D638; paper and paperboard to ISO 1924-2, ASTM D828, or GB/T 12914. The choice also depends on the target market and any customer-specified method, and accredited third-party laboratories can advise on the most appropriate procedure.

Question: Why must specimens be tested in both machine and transverse directions?

Answer: Most packaging films and papers are anisotropic because of manufacturing orientation. Machine-direction strength can be substantially higher than transverse-direction strength, and package performance depends on both. Testing only one direction can significantly overestimate or underestimate the mechanical capability of the material.

Question: How many specimens are required for a valid result?

Answer: Standards generally require a minimum of five valid specimens per direction. Specimens that break in or at the grips are considered invalid and must be replaced, because such failures reflect grip effects rather than the true strength of the material.

Question: What happens if the specimen keeps slipping or breaking in the grips?

Answer: Laboratories address this by changing grip face material or pressure, reducing the crosshead speed, adding reinforcing tabs at the specimen ends, or switching to dumbbell-shaped specimens where the standard permits, ensuring that rupture occurs within the gauge length so the measured force represents the true breaking force.

Question: How is breaking force testing related to seal strength testing?

Answer: They are complementary but distinct tests. Breaking force characterizes the substrate itself, while seal strength testing to ASTM F88 measures the force needed to peel or break a sealed fin or lap. Comparing the two values confirms whether the weakest link in a finished package lies in the base material or in the seal, which is essential information for troubleshooting package failures.