Overview
EN ISO 5402-2:2015 - Leather: Determination of flex resistance, Part 2 (Vamp flex method) specifies a laboratory method to assess the wet or dry flex resistance of leather and surface finishes. Applicable to all leathers below 3.0 mm thickness, this standard defines the vamp‑flex test used widely in footwear and leather goods quality assessment to evaluate durability where repeated bending occurs.
Key topics and technical requirements
- Test principle: A test piece is folded over two inverted “V” clamps and flexed by reciprocating the clamps to produce a central downward crease and surrounding upward creases; damage is inspected periodically.
- Apparatus essentials:
- Two inverted “V” clamps aligned on one axis with minimum separation (9.5 ± 1.0) mm.
- Clamp geometry: internal angle (40 ± 1)°, truncated tip radius (6.4 ± 0.5) mm.
- Oscillating motion between 9.5 mm and 19.0 ± 1.5 mm at (300 ± 30) cycles/min; counter to record cycles.
- Press knife (square inner wall 64 ± 1 mm), magnifier (4–6×), and distilled/deionized water (ISO 3696 grade 3) for wet tests.
- Sampling & preparation:
- Cut test pieces parallel and perpendicular to the backbone per ISO 2418 and condition per ISO 2419.
- Wet tests: rub ~1 ml distilled/deionized water into the flesh surface and re‑wet every 25,000 cycles.
- Test procedure & cycle options:
- Ensure correct folding, run to specified cycle counts. Typical inspection points:
- Dry flex: 50,000; 100,000; 250,000; 500,000; 1,000,000 cycles.
- Wet flex: 50,000; 100,000 cycles (inspect and re‑wet every 25,000 cycles).
- Damage assessment: look for creasing, cracking (inward/outward folds), delamination/flaking, edge cracking and spue (wet tests). Test report must record test conditions, number of cycles, damage at inspections and deviations.
Applications and users
Practical uses and beneficiaries of EN ISO 5402-2:2015:
- Footwear manufacturers and component suppliers - assessing vamp (upper) durability and specifying leather for shoes.
- Leather tanneries and finishers - R&D and quality control of finished leathers and coatings.
- Independent testing laboratories - conformity testing, comparative performance data.
- Product designers, QA managers and standards compliance teams - material selection and failure analysis for bent or flexing applications (uppers, straps, gloves).
Related standards
- ISO 5402-1 (Flexometer method) - complementary flex testing technique.
- ISO 2418 - sampling location for leather tests.
- ISO 2419 - sample preparation and conditioning.
- ISO 3696 - laboratory water quality for wet testing.
EN ISO 5402-2:2015 (Vamp flex method) provides a repeatable, industry‑accepted procedure for measuring flex resistance of thin leathers - key for predicting in‑use durability and ensuring product quality.