Overview
ISO 844:2021 specifies laboratory methods for determining the compression properties of rigid cellular plastics. The standard defines two test procedures and the required apparatus, specimen preparation and measurement practices to obtain repeatable values for compressive strength, compressive stress at 10% relative deformation, and the compressive modulus (nominal and measured). It is the authoritative reference for compression testing of rigid foam materials used in insulation, structural components and other applications where compressive behaviour matters.
Key topics and technical requirements
- Scope of measurement
- Compressive strength (σm), compressive stress at 10% nominal relative deformation (σC10), nominal compressive modulus (EC) and compressive modulus (E).
- Two procedures
- Procedure A: uses crosshead motion (machine displacement) to determine compressive strength, σC10 and nominal modulus (EC).
- Procedure B: uses an extensometer or direct strain-measuring device (contact or optical) to determine compressive strength and compressive modulus (E).
- Apparatus requirements
- Compression-testing machine with two polished, parallel plates; recommended surface roughness Ra ≤ 0.4 µm and plate thickness t ≥ 8 mm.
- Force sensor meeting class 1 accuracy per ISO 7500-1.
- Displacement accuracy: continuous measurement with ±5% or ±0.1 mm (whichever is more accurate).
- Extensometer (Procedure B) compliant with class 1 of ISO 9513; gage length depends on specimen thickness (table provided in the standard).
- Test specimens
- Preferred specimen: 100 × 100 × 50 mm prism (±1 mm).
- Acceptable specimen area range: minimum 25 cm² to maximum 230 cm².
- Minimum thickness normally 20 ±1 mm (exceptions for moulded skins - minimum 10 mm).
- Parallelism tolerance: distance between faces must not vary by more than 1%.
- Calibration & references
- Machine and measuring devices to be calibrated per ISO 7500-1 (force) and ISO 9513 (extensometer/displacement).
- Conditioning and dimensional measurement referenced to ISO 291 and ISO 1923.
Applications and who uses this standard
ISO 844:2021 is used by:
- Manufacturers and quality-control laboratories for batch acceptance and production control of rigid cellular plastics (foams).
- Materials R&D teams for product development and performance comparison.
- Test laboratories and certification bodies to generate compliant test reports.
- Specifiers, architects and engineers who require validated compressive property data for insulation, packaging support, structural cores (e.g., sandwich panels) and transport cushioning.
Practical benefits include consistent, reproducible compression data for material selection, design validation, compliance testing and supplier benchmarking.
Related standards
- ISO 291 - Standard atmospheres for conditioning and testing
- ISO 1923 - Determination of linear dimensions (cellular plastics)
- ISO 7500-1 - Calibration and verification of force-measuring systems (tension/compression machines)
- ISO 9513 - Calibration of extensometer systems
Keywords: ISO 844:2021, rigid cellular plastics, compression properties, compressive strength, compressive modulus, compression testing, extensometer, test specimens, foam testing.
