Overview
ISO 17236:2025 - "Leather - Physical and mechanical tests - Determination of extension set" specifies a repeatable laboratory method to measure the permanent elongation (extension set) of flexible leathers. Intended primarily for upholstery leather, the method is applicable to all flexible leathers and provides a standard procedure for specimen preparation, conditioning, test execution and result reporting.
Key topics and technical requirements
- Test principle: A specimen is cyclically stretched to a defined load and the permanent extension after unloading is expressed as a percentage of the original gauge length.
- Specimen preparation & orientation: Cut six test pieces (three parallel and three perpendicular to the backbone) using a press knife; measure thickness at three points and use the mean thickness.
- Conditioning: Condition specimens in the reference standard atmosphere per ISO 2419 before testing; return to conditioning if delayed longer than 30 minutes.
- Apparatus:
- Tensile testing machine with uniform crosshead speed of (50 ± 5) mm/min and force-recording accuracy to Class 2 of ISO 7500-1:2018.
- Jaws that prevent slippage (minimum 30 mm clamping face).
- Thickness gauge per ISO 2589, ruler, stopwatch and press knife.
- Test cycle:
- Clamp specimen with ~25 mm in each jaw and set jaws 200 mm apart.
- Apply an instrumental pre-load (1.0 N may be used; alternatives by agreement).
- Run until a load of 20.0 N ± 0.5 N is reached, hold for 10 s ± 1 s, return to start - repeat for a total of five cycles.
- After the final cycle lay specimen flat and measure the distance between marks after 60 s ± 5 s.
- Result calculation: Percentage extension set = (final distance − initial distance) ÷ initial distance × 100.
- Test report: Must reference ISO 17236:2025 and include identification of specimen, pre-load, mean extension set in each direction, mean thickness, conditioning atmosphere, deviations and test date.
Applications
- Quality control and production acceptance testing of upholstery and flexible leathers.
- Material specification and supplier qualification for furniture, automotive interiors, footwear components and leather goods where residual elongation affects fit, performance or aesthetics.
- R&D and comparative evaluations to optimise tanning, finishing or mechanical treatments that affect permanent deformation.
Who should use this standard
- Leather manufacturers and finishers
- Independent testing laboratories and QA teams
- Product engineers in upholstery, automotive interior and furniture industries
- Standards committees and procurement/specification writers
Related standards
- ISO 2418 - Position and preparation of specimens
- ISO 2419 - Specimen and test piece conditioning
- ISO 2589 - Thickness measurement
- ISO 7500-1:2018 - Calibration and verification of tension/compression testing machines
Keywords: ISO 17236:2025, leather extension set, extension set test, upholstery leather testing, tensile testing machine, leather physical tests, leather conditioning.
