Overview
ISO 1856:2018 - Flexible cellular polymeric materials - Determination of compression set - specifies standardized test methods to measure the compression set (permanent deformation after compression) of flexible cellular polymeric materials. The standard applies to latex and polyurethane foams with thickness greater than 2 mm and defines three test methods (A, B and C), sampling, conditioning, measurement and reporting requirements for reliable, repeatable results.
Key topics and technical requirements
- Scope: Applies to latex and polyurethane foams > 2 mm thickness. Tests require familiarity with normal laboratory practice.
- Test pieces: Nominal dimensions (50 ± 1) mm × (50 ± 1) mm × (25 ± 1) mm. Surfaces must be parallel and free from contamination and side skin. For thin materials (min 2 mm) use assemblies of plies interleaved with photographic glass slides so total thickness ≥ 25 mm.
- Number of samples: Five test pieces (or five assemblies for thin materials).
- Conditioning: Minimum conditioning of 16 h in atmospheres per ISO 23529: either (23 ± 2) °C / (50 ± 5) % RH or (27 ± 2) °C / (65 ± 5) % RH. Do not test earlier than 72 h after manufacture unless validated exceptions apply.
- Methods:
- Method A - Compression at (70 ± 1) °C for (22 ± 0.2) h. Compression level typically (50 ± 4) % or (75 ± 4) % of thickness; 90 % may be agreed for special cases. Recovery for (30 ± 5) min at conditioning temperature before remeasurement.
- Method B - Compression at the conditioning temperature for (72 ± 0.2) h (same procedure as A otherwise).
- Method C - Test under time, temperature and compression level agreed between parties (custom conditions).
- Apparatus & measurement: Compression device with flat plates and spacers; thickness measurement in accordance with ISO 1923. For thin-foam assemblies use photographic glass mounting slides (1–1.5 mm thick, side 50–55 mm).
- Calculation: Compression set (%) = ((d0 − dr) / d0) × 100, where d0 = original thickness and dr = recovered thickness after test.
- Reporting: Include reference to ISO 1856:2018, material description, conditioning, method used, individual values, median, test conditions (compression level, time, temperature) and any deviations.
Applications and users
ISO 1856:2018 is used by:
- Foam manufacturers and quality control laboratories verifying compression set performance of latex and polyurethane foams.
- Product designers and specifiers in bedding, upholstery, automotive seating, footwear insoles and acoustic/thermal insulation where resilience and long‑term thickness retention are critical.
- Test laboratories issuing compliant test reports for procurement, compliance and R&D comparisons.
Related standards
- ISO 1923 - Determination of linear dimensions (used for thickness measurement)
- ISO 23529 - Preparation and conditioning of test pieces for physical tests
Keywords: ISO 1856:2018, compression set, latex foam, polyurethane foam, flexible cellular polymeric materials, compression test, foam conditioning, ISO 1923, ISO 23529.
