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The indentation hardness of flexible cellular materials is a measure of their load-bearing properties. ISO 2439:2008 specifies four methods (A to D) for the determination of indentation hardness and one method (E) for determination of compressive deflection coefficient and hysteresis loss rate of flexible cellular materials. Annex A provides a summary of test parameters and typical force-indentation graphs obtained with these methods.

These five methods are applicable only to latex foam, urethane foam and PVC foam of the open-cell type. The methods specified can be used for testing finished articles and for the characterization of bulk material.

ISO 2439:2008 specifies the following methods:

1. Method A — Determination of the 40 %/30 s indentation hardness index, which gives a single indentation measurement for laboratory test purposes;
2. Method B — Determination of the 25 %-40 %-65 %/30 s indentation hardness characteristics, which provides information about the shape of the hardness indentation curve;
3. Method C — Determination of the 40 % indentation hardness check, which is a quick procedure suitable for quality control testing;
4. Method D — Determination of the 25 %/20 s low indentation hardness index, which is a quick procedure suitable as an inspection test;
5. Method E — Determination of the compressive deflection coefficient and hysteresis loss rate, which gives additional information about the load-bearing properties of materials.

The results obtained by these methods relate only to the test conditions specified and cannot, in general, be used directly for design purposes.