ISO 3379 Leather Surface Distension & Strength (Ball-burst/ Lastometer Test)

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ISO 3379 Leather Ball Burst Tester | Surface Distension & Strength Test Machine | UnitedTest

UnitedTest manufactures professional ISO 3379 compliant leather ball burst testers, designed to accurately evaluate surface distension, stretch resistance, and surface failure strength for all types of flexible leather materials in footwear and leather goods quality control.

ISO 3379 Leather — Determination of distension and strength of surface (ball burst method) is an international standard that specifies reliable ball burst testing procedures for leather surface performance assessment. This test method professionally evaluates the multi-directional stretch resistance and surface failure performance of leather grain and coating layers, identifying structural weaknesses under distension stress.

Suitable for all flexible leather materials, the ISO 3379 ball burst test is particularly authoritative for testing and verifying the lastability of footwear upper leather. It provides repeatable, standardized mechanical performance data to help manufacturers inspect leather quality, optimize material selection, and ensure durability for shoe uppers and finished leather products.

Test Principle:

Leather upper materials undergo multi-directional stretching during shoe lasting, furniture upholstery forming, and automotive interior shaping—uniaxial tensile tests cannot replicate this real biaxial stress state.

ISO 3379’s ball burst mechanism simulates uniform radial tension: the clamped circular sample restricts edge movement, while the central hemispherical indenter produces equal biaxial tensile stress across the grain surface. As the indenter advances, surface distension increases gradually. The grain coating or leather grain will first crack under critical biaxial strain (grain crack distension), then the whole substrate breaks at higher displacement (burst distension). By recording displacement and force at both failure stages, the standard quantifies two core surface performance metrics: surface ductility and grain burst strength.

Specific Test Method

The standard adopts the ball burst (lastometer) method, a biaxial bulge tensile test rather than uniaxial tension. A circular leather specimen is rigidly clamped around its edge, then a fixed-diameter hemispherical steel ball indenter pushes upward from the flesh side to stretch the grain surface evenly in all radial directions. Two critical failure points are recorded during continuous stretching:

Grain crack point: The first visible tiny crack (<0.5 mm) on the top grain/finished coating; record corresponding distension displacement and force.

Full burst point: Complete through-thickness rupture of the specimen; record maximum distension and burst load.

Test Equipment of ISO 3379 Leather Surface Distension & Strength (Ball-burst/ Lastometer Test):

Component	Specification
Universal Testing Machine	Recommend UnitedTest WDW series universal testing machine. Motorised vertical piston with constant test speed control, displacement measurement accuracy ±0.05 mm. Force sensor: Load cell to continuously record applied compressive force with high precision.
Ball Clamping fixture	Circular serrated anti-slip clamping ring with a central aperture of 25.0 mm ±0.5 mm, fully securing specimen edges without slippage during loading. Hemispherical steel indenter: Hardened polished steel ball with diameter 6.25 mm ±0.05 mm, mounted on a vertical movable piston.
Accessories	Standard circular punch, thickness gauge, conditioning cabinet complying with ISO 2419.

Component

Specification

Universal Testing Machine

Recommend UnitedTest WDW series universal testing machine.

Motorised vertical piston with constant test speed control, displacement measurement accuracy ±0.05 mm.

Force sensor: Load cell to continuously record applied compressive force with high precision.

Ball Clamping fixture

Circular serrated anti-slip clamping ring with a central aperture of 25.0 mm ±0.5 mm, fully securing specimen edges without slippage during loading.

Hemispherical steel indenter: Hardened polished steel ball with diameter 6.25 mm ±0.05 mm, mounted on a vertical movable piston.

ISO 3379 Leather Surface Distension

Accessories

Standard circular punch, thickness gauge, conditioning cabinet complying with ISO 2419.

Test Specimen Information:

Sampling Rule

Sample raw leather according to ISO 2418: Cut representative areas avoiding defects, edges, folds, brand marks, or damaged zones.

Minimum 3 valid circular specimens per test batch for repeatability testing.

Specimen Geometry

Perfect circular discs cut to a diameter larger than the 25 mm clamping aperture (standard punch size covers full clamping range).

Details Test Procedure of ISO 3379 Leather Surface Distension & Strength (Ball-burst/ Lastometer Test):

Sampling: Cut representative leather areas following ISO 2418, punch out ≥3 circular specimens.

Conditioning: Place specimens in standard climate chamber for minimum 24 h to stabilise moisture.

Thickness measurement: Record thickness of each specimen via ISO 2589 gauge.

Equipment setup: Calibrate ball burst tester, confirm indenter size, clamping aperture, and test speed set to 0.20 mm/s.

Specimen mounting: Lay specimen flat with grain side up; fasten clamping ring tightly to eliminate edge slipping.

Pre-test check: Confirm steel ball indenter touches the exact centre of the flesh side without preloading.

Start test: Activate piston upward movement at constant speed; observe grain surface via magnifier continuously.

Record grain crack data: Mark displacement and force the moment the first tiny grain crack appears.

Continue loading: Keep indenter advancing until full through-specimen burst rupture. Record burst distension and maximum burst force.

Unload & remove specimen: Retract piston, take out tested sample, inspect failure morphology.

Repeat test: Complete all 3 replicate specimens under identical parameters.

Data processing: Average crack distension, burst distension, crack load, burst load; compile full test report as required by ISO 3379.

Test Parameters and Stipulations:

Clamping opening inner diameter: 25.0 mm (tolerance ±0.5 mm)

Indenter hemisphere diameter: 6.25 mm (tolerance ±0.05 mm)

Vertical piston advancing speed: 0.20 mm/s (tolerance ±0.05 mm/s, constant speed without acceleration)

Required specimen quantity: ≥3 replicates per material

Termination criteria: Stop test immediately upon first grain crack observation; continue to full burst for complete dataset collection.

No specimen slippage is allowed during testing; serrated clamping surfaces are mandatory to eliminate slip error.

The leather grain/finished surface must face upward (toward the operator’s observation side); indenter pushes from the flesh backside only.

If coating peels off before grain cracking, record coating delamination as a separate failure mode in the test report.

Industrial Application Fields

Footwear industry (primary application): Evaluate upper leather lastability—core indicator for shoe manufacturing. Predicts if leather will crack during shoe lasting, toe-cap shaping, or daily walking bending. Covers cowhide, sheepskin, goatskin, synthetic-finished shoe uppers, boot leather, and children’s shoe leather.

Automotive interior leather: Test seat, door panel, and steering wheel leather resistance to stretching during hot forming and long-term occupant compression.

Furniture & upholstery leather: Assess sofa, armchair, and cushion leather anti-crack performance under continuous body pressure and surface stretching.

Luxury leather goods: Handbag, wallet, luggage leather quality control to avoid surface cracking after moulding and long-term use.

Garment leather: Light leather for jackets, skirts to verify surface ductility under wear deformation.

Related Standard:

ISO 3379	Leather — Determination of distension and strength of surface (ball burst method)
QB/T 2712	Leather-Physical and mechanical tests-Determination of distension and strength of grain-Ball burst test
DIN 53325	Testing of leather; ball compression test for determination of grain expansion capacity and the force of fracture with the lastometer
BS 3144	Methods of sampling and physical testing of leather Section 8 Measurement Of distention and strength of grain by the ball burst test
SATRA TM166	Slide fastener burst strength
SATRA TM24	Lastometer ball burst test
ASTM D2210	Standard Test Method for Grain Crack and Extension of Leather by the Mullen Test
ISO 17693	Footwear - Test methods for uppers - Resistance to damage on lasting
GB/T 3903.38	Footwear - Test methods for uppers - Resistance to damage on lasting
EN 12747	Footwear - Test methods for insoles - Abrasion resistance
EN 13520	Footwear - Test methods for uppers, lining and insocks - Abrasion resistance;
ISO 3376	Leather — Determination of tensile strength and elongation

Keywords: UnitedTest ISO 3379 tester, ISO 3379 leather ball burst tester, leather surface distension strength test machine, footwear leather lastability testing equipment, ISO 3379 multi-directional stretch resistance test for leather, leather grain coating surface failure ball burst test, flexible leather surface distension strength analyzer, footwear upper leather lastability quality test machine

WDW Series Computer Control Electronic Universal Testing Machine made by UNITEDTEST range from 100N to 600KN load capacity with various models like single columns, table type, door frame type etc., is used to perform tension, compression, flexure/bending, shearing, peeling etc., test for metal and nonmetal specimens. Matched with UNITEDTEST design and produced various test fixture, like peel, flexure, puncture, tear, pneumatic grip, belt tension etc., this UTM can be used to almost all materials include but not limited to steel rod, rubber, steel wire, plastic, seat belt, textile, wood, panel etc., mechanical performance inspection.

ASTM D3787 Ball Burst Puncture Test Fixture is a standardized attachment for constant-rate-of-traverse (CRT) tensile testing machines, used to determine the bursting strength of textile fabrics by forcing a polished steel ball through a clamped specimen at a constant rate until rupture.

Q1: What is ISO 3379 also known as, and what does it measure?

A1: ISO 3379:2024 is titled Leather – Determination of distension and strength of surface (ball burst method), also called the IULTCS/IUP 9 lastometer test. It measures two key surface properties of leather under biaxial stretching:

Grain crack distension & force (the point the leather grain/topcoat first cracks)

Full burst distension & maximum burst load (complete penetration rupture of the leather substrate)

It evaluates how well leather surface withstands uniform multi-directional stretching.

Q2: Why is ISO 3379 different from the uniaxial tensile test ISO 3376?

A2: ISO 3376 applies one-way linear tension only. Real leather usage (shoe lasting, upholstery moulding) creates equal radial biaxial stress. The ball burst fixture clamps a circular sample and pushes a hemispherical ball to stretch the leather evenly in all directions, replicating real forming stress states that uniaxial testing cannot simulate.

Q3: Why is the ISO 3379 test critical for leather materials?

A3: It predicts production failure: Low grain distension means leather will crack during shoe lasting, furniture hot forming or automotive interior shaping, causing mass waste.

It evaluates finished coating ductility: Crack data judges if topcoat finishes are flexible enough for daily repeated deformation.

It provides a global unified benchmark: Tanneries, manufacturers and buyers across countries use identical test rules to compare leather quality fairly.

It ensures end-product durability: Leather with poor burst performance develops permanent cracks after repeated bending, sitting or stretching during consumer use.

It supports compliance: Footwear, automotive and furniture brand specifications often require ISO 3379 test reports for incoming material quality approval.

Q4: What are the mandatory dimensional requirements for the ball indenter and clamping ring?

A4: Clamping central aperture: 25.0 mm ±0.5 mm

Hemispherical steel indenter diameter: 6.25 mm ±0.05 mm

Deviations outside these tolerances will produce invalid distension and force data, and the test results cannot be accepted for compliance reporting.

Q5: Can I use a generic tensile machine to run ISO 3379 instead of a dedicated lastometer?

A5: Only if the tensile machine is fitted with a certified ISO 3379-specific ball burst fixture that meets all dimensional, speed and clamping requirements. A standard uniaxial jaw setup cannot create uniform biaxial bulge stress, so raw tensile equipment without the special fixture is not compliant.

Q6: Why must the clamping ring have serrated anti-slip surfaces?

A6: Any slippage of the leather specimen during the test will artificially increase measured distension values, leading to falsely optimistic performance results. Serrated clamping eliminates edge sliding to guarantee accurate crack and burst displacement readings.

Q7: How many specimens are required per leather batch, and why?

A7: A minimum of three valid circular specimens must be tested. Leather has natural structural variations across hides; three replicates average out random material defects to deliver statistically reliable test results. Any outlier caused by scratches, holes or uneven coating must be excluded from the final average.

Q8: What if the leather coating delaminates before any grain crack forms?

A8: Record coating delamination as a separate failure mode in the official test report. This indicates poor coating adhesion rather than insufficient surface distension, and brands/tanneries will use this result to adjust finishing formulations.

Q9: Which side of the leather faces up during testing – grain or flesh?

A9: The grain/finished surface must face upward (toward the operator’s magnifier). The steel ball indenter pushes upward from the flesh side. Reversing the sample flips the stress distribution on the topcoat and invalidates grain crack detection.

Q10: How do tanneries use ISO 3379 results to improve leather quality?

A10: Low grain distension signals stiff grain or brittle finishing coatings. Tanneries adjust retanning, fatliquoring and topcoat formulation to increase surface flexibility. Higher crack distension values improve leather processability during manufacturing and extend the service life of finished leather products.

Q11: What is the standard test speed for ISO 3379, and what error margin is allowed?

A11: The piston advance speed is fixed at 0.20 mm/s ±0.05 mm/s. Faster speeds raise measured burst force and reduce crack distension; slower speeds allow stress relaxation, lowering force values. Non-compliant speed makes results unfit for standard reporting.

Q12: Do I stop the test once the first grain crack appears?

A12: You record displacement and force at the first visible grain crack, then continue running the test until full through-thickness burst rupture. Both sets of data are required for a complete ISO 3379 test report, as grain crack performance and full burst strength are separate critical quality indicators.

Q13. What is the difference between a "Crack" and a "Burst"?

Crack: Defined as a small surface split in the grain or finish, typically less than 0.5 mm. This is usually the most critical result for quality control, as it indicates the finish or grain has failed even if the leather is still holding together.

Burst: The complete rupture of the entire thickness of the leather specimen. This measures the ultimate strength of the substrate material.Q14. What is the "Lastometer"?

The "Lastometer" is simply the common industry name for the testing machine used to perform the ISO 3379 ball burst test. The term comes from the word "Last" (the foot form used in shoemaking) + "Meter" (to measure).

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