Polyurethane Foam Testing: A Quick Guide

Since its first production run over 50 years ago, polyurethane foam has continued to undergo rigorous, high-quality testing. As an incredibly versatile material that can be manufactured to hold a diverse range of properties, it's unsurprising that all forms of polyurethane product are tested.

Why foam is tested

Thorough testing accurately measures and records every characteristic of a foam material, which lets manufacturers allocate the foam to its rightful application. For example, foam inserts used inside flight cases need to be measured for shock absorbency to ensure they withstand the demands of air freight. Our guide to foam density, weight and firmness covers how these properties relate.

Flex fatigue

The most universal test is flex fatigue, designed to gauge a foam's resilience by calculating durability through repetitive compressions. Using a dedicated machine, the material is pushed to its limits through thousands of compressions, from which the percentage of IFD (Indentation Force Deflection, also known as ILD) loss is measured against the foam's original height. Longer tests give a better overview of overall durability, while shorter, standard tests show how much firmness or density will be lost through initial use. Some industry machines can run a range of compression tests at once.

Hysteresis

Second to flex fatigue is hysteresis, used to determine how well a foam retains its original firmness. Under laboratory conditions, a sample is indented by 25% and its firmness measured, then indented to 65% and re-measured, before being released back to 25% without allowing the foam to fully expand. This is the crucial part: although the 25% indentation is maintained, the foam won't recover its full original firmness, and the amount it does recover gives a solid indication of overall durability.

Firmness and support factor

Two further tests – firmness and support factor – assess whether a foam can support weight. Usually a higher-density foam has a better support factor, though this varies. As with hysteresis, the foam is compressed to 25% and then to 65% of its height, taking a second IFD measurement; a greater difference between the two means a higher ability to support weight. The overall support factor is the ratio of the 65% IFD to the 25% IFD, while overall firmness is the force in pounds needed to compress the sample to 25% of its original height.

There's a huge array of tests, from resilience and roller shear to airflow, all used to diagnose a foam's optimal performance – too many to explore in full here. For more on the wider context, see our guide to polyurethane foam history, manufacture and testing, or contact us to discuss your requirements.