Overview
ISO 20874:2018 specifies the standardized test method for determining the needle tear strength of footwear outsoles, regardless of the material composition. This international standard is essential for manufacturers, quality control laboratories, and footwear developers aiming to assess the tear resistance of outsole materials under controlled and reproducible conditions. The second edition of this document updates and replaces the original 2001 version to reflect improved technical requirements.
The standard provides a detailed procedure to measure the maximum force required to tear an outsole material by a needle, normalizing the result by the specimen’s thickness. This allows consistent comparison of outsole durability across different types of materials including polymeric, elastomeric, semi-expanded, cellular, or leather outsoles.
Key Topics
-
Scope and Application: ISO 20874:2018 applies universally to outsole materials used in footwear, making it relevant across a wide range of shoe manufacturing processes.
-
Test Specimen Preparation: Outsole samples are conditioned and cut into standardized strips (typically 50 mm x 20 mm) with thicknesses depending on the material type:
- 2.0 mm ± 0.2 mm for polymeric/elastomeric compact outsoles
- 4.0 mm ± 0.2 mm for semi-expanded/cellular outsoles
- Original thickness maintained for leather outsoles
Specimens may retain original surfaces ("skins") to reflect real-world conditions.
-
Testing Apparatus:
- A tensile-testing machine complying with ISO 7500-1 ensures accurate force measurement at a controlled traverse rate of 100 mm/min ± 10 mm/min.
- A steel needle of 1 mm diameter is used to initiate tearing, combined with a specially designed clamping device to hold the specimen securely during testing.
- Thickness gauge with controlled pressure for precise thickness measurement of the test piece.
-
Test Procedure:
The needle is inserted 5 mm from the specimen’s edge perpendicular to the surface. The specimen is stretched until the needle tears through the material. The maximum force observed during this tear is recorded and normalized by the specimen thickness to calculate the needle tear strength (N/mm).
-
Results Expression and Reporting:
Results are expressed as the average of three test specimens, reported in newtons per millimeter of thickness. The test report must include:
- Reference to ISO 20874:2018
- Detailed sample description (material, style, color)
- Specimen type and thickness
- Test results and conditions (including atmospheric conditions)
- Any deviations from the protocol
Applications
The needle tear strength test described in ISO 20874:2018 is critical for:
- Footwear Design and Quality Assurance: Ensuring outsole materials meet durability standards to resist puncture and tearing; improving product longevity.
- Material Selection and Development: Comparing tear resistance of new polymers, rubbers, composites, or leathers in casual, sports, and safety footwear.
- Compliance and Certification: Supporting claims for product performance in line with international footwear standards and consumer safety requirements.
- Research and Innovation: Assisting R&D to optimize outsole formulations and constructions based on empirical strength data.
Related Standards
ISO 20874:2018 references and complements several important standards and guidelines in footwear testing and material evaluation:
- ISO 7500-1: Calibration and verification of static uniaxial testing machines, ensuring accuracy and reliability of tensile testing equipment.
- ISO 17709: Guidelines for sampling location, preparation, and conditioning of footwear test samples to guarantee uniformity before testing.
- ISO 18454: Specifies standard atmospheres for conditioning and testing footwear components, critical to test repeatability and comparability.
By integrating ISO 20874:2018 with related footwear standards, manufacturers and testing labs can implement robust quality control processes, producing durable, safe, and high-performance footwear products.
Keywords: ISO 20874:2018, needle tear strength, outsole testing, footwear standards, tensile testing, outsole durability, polymeric outsole, leather outsole, footwear material testing, tear resistance test, shoe outsole quality control
