ISO 24999:2008

Overview

ISO 24999:2008 specifies a laboratory method for determining the fatigue behaviour of flexible cellular polymeric materials (foams) by a constant‑strain compression procedure. The standard measures the loss in thickness after repetitive compression and is intended primarily for quality control and comparative assessment of flexible polymeric cellular materials used in load‑bearing and cushioning applications.

Key topics and requirements

• Scope: Measures thickness loss when specimens are repetitively compressed to a fixed strain; complementary to constant‑stress methods (ISO 3385).
• Test principle: Apply constant strain cyclically to the full surface of the test piece, then measure final thickness to compute percentage thickness loss.
• Apparatus: Compression machine with two square parallel plates (one oscillating), ventilated lower plate (air‑vent holes) and adjustable spacing to avoid edge effects; capable of testing multiple specimens simultaneously.
• Specimens:
  • Parallelepiped shape, minimum 50 mm × 50 mm × 20 mm.
  • Three test pieces per test; specimens with cellular orientation must have compression direction agreed between parties.
• Conditioning:
  • Do not test earlier than 72 h after manufacture unless validated at 16 h or 48 h.
  • Pre‑test conditioning for at least 16 h at either (23 ± 2) °C / (50 ± 5) % RH or (27 ± 2) °C / (65 ± 5) % RH (shorter times permitted for QC).
• Test cycle:
  • Compress for 80 000 cycles at (60 ± 5) cycles/min.
  • Stroke set to produce 50% compression of original thickness of the thinnest specimen.
  • Allow 30 min ± 5 min recovery in conditioning atmosphere before final thickness measurement.
• Results: Percentage thickness loss calculated and expressed as the median of three specimens.
• Reporting: Test report must reference the standard and include material description, conditioning, specimen size/orientation, median thickness loss and test date.
• Precision: Annex A summarizes interlaboratory precision (repeatability/reproducibility) based on a multi‑laboratory study.

Applications and users

ISO 24999:2008 is useful for:

• Manufacturers and quality‑control laboratories of flexible polymeric foams (e.g., polyurethane foam).
• Product engineers assessing long‑term cushioning and load‑bearing performance.
• Specifiers and procurement teams requiring standardized fatigue data for foam selection.
• R&D teams comparing material formulations or processing effects on compression fatigue.

Practical benefits include simultaneous testing of multiple specimens (higher throughput) and providing data that, together with constant‑load methods, helps predict end‑use performance.

Related standards

• ISO 3385 - Constant‑load fatigue (complementary method)
• ISO 5999 - Material classification for load‑bearing polyurethane foam
• ISO 1923 - Measurement of linear dimensions (thickness measurement)
• ISO 23529 / ISO/TR 9272 - Conditioning and precision guidance

Keywords: ISO 24999:2008, constant‑strain, flexible cellular polymeric materials, foam fatigue testing, thickness loss, compression testing, quality control.