How to Perform a Foam Fatigue Test?

When a mattress, a seat cushion, or a car seat is used for years, does it keep its original support, or does it collapse? The answer to that question comes from the lab in a matter of hours instead of days of real-world use: the foam fatigue test. In this article, we walk through what the test is, which standards it follows, and how to read the results, step by step.

What is a foam fatigue test?

A fatigue test measures how well flexible foam holds up over time under repeated load. The device applies pressure to the sample thousands of times, and at the end of this cycle, it determines the loss in the foam’s thickness and firmness. The goal is to estimate the material’s long-term real-world behavior in an accelerated way; for example, simulating the wear that years of sitting down on and getting up from a car seat would cause.

An important point: fatigue testing is used to compare materials under identical conditions. The measured loss may not correspond exactly to real service life, but it remains the most reliable way to compare different foam formulations objectively and repeatably.

Which standards is it performed to?

There are two internationally recognized references for foam fatigue testing:

• ISO 3385: Constant-load pounding fatigue test
• ASTM D3574 Test I3: Constant-force pounding fatigue test (equivalent to ISO 3385)

Both standards cover flexible polyurethane and latex-based foams used in upholstery and load-bearing applications.

The test method, step by step

1. Sample preparation and conditioning

The standard sample is cut as a rectangular prism measuring 380 × 380 mm on each side, with a thickness of 50 mm (±2 mm). Before testing, the sample is conditioned for at least 12 hours at 23 °C and 50% relative humidity. Skipping this step makes the results non-repeatable.

2. Measuring the initial values

Two values are recorded before the fatigue cycle begins:

• Initial thickness (measured with light contact force, after pre-flexing)
• 40% IFD firmness value: the force required to compress the foam to 40% of its thickness (per ISO 2439 / ASTM D3574 Test B)

These two values are the “before” snapshot of the test.

3. Applying the fatigue cycle

An indenter approximately 250 mm in diameter repeatedly applies a specific force to the sample. Typical parameters:

• Applied force: 750 N (±20 N)
• Cycle rate: approximately 70 strokes per minute (≈1.17 Hz)
• Number of cycles: 8,000 cycles or more, depending on the application

4. Measuring the results

After the cycle is completed, the sample is re-measured and three loss values are calculated:

• Thickness loss (%): how much the foam has collapsed
• Firmness loss (40% IFD loss): how much support has weakened
• Structural degradation: visual inspection for cracking, splitting, or deformation

What do the results mean?

The lower the thickness and firmness loss, the more durable the foam. For example, a premium mattress foam loses far less thickness than a cheaper alternative over the same number of cycles. For manufacturers, this data provides concrete grounds for formulation development, supplier comparison, and the warranty commitments made to customers.

In which industries is fatigue testing critical?

In mattress, furniture upholstery, and automotive seat manufacturing, fatigue performance directly determines product lifespan. For manufacturers supplying foam to these industries, regular fatigue testing is the foundation of quality assurance and brand reliability.

Dynamic fatigue vs. compression set: two different tests

These two tests are often confused. In a compression set test (ISO 1856), the sample is held under constant, uninterrupted compression for a set time, and the thickness it fails to recover is measured. In a dynamic fatigue test (ISO 3385), the foam is loaded and unloaded thousands of times. The first simulates steady load during storage and transport; the second simulates everyday repeated use.

Key parameters of ISO 3385

In ISO 3385, the sample’s thickness and hardness are measured first. It is then pounded with a constant load 80,000 times at 70 ± 5 strokes per minute. After a recovery period, the measurements are repeated and the loss in thickness and loss in hardness are calculated as percentages. ASTM D3574 Test I3 describes a comparable constant-force pounding method.

Common mistakes in fatigue testing

• Not recording the initial values carefully. The result isn’t an absolute value but a loss relative to the starting point.
• Measuring as soon as the cycles end. Foam recovers part of its thickness as it rests, so the recovery time in the standard must be respected.
• Comparing tests run at different cycle counts or loads. Such comparisons are meaningless.
• Skipping conditioning. The sample should be held at 23 ± 2 °C and 50 ± 5% relative humidity before and after the test.

Frequently asked questions

Does higher density reduce thickness loss?

Often yes, because density is linked to durability. It isn’t the only factor, though; formulation and cell structure also affect the result. More detail: foam density test standards.

What is the difference between a fatigue test and a resilience test?

A resilience test measures how the foam behaves at a single moment while it’s new. A fatigue test shows how much of that behavior is left after an accelerated service life.

To see where fatigue testing fits among the other foam tests, read our foam testing guide.

Precise, repeatable fatigue testing with Vilutra

The MK-1090 Foam Fatigue Tester applies thousands of cycles under constant load in a controlled manner, in line with ISO 3385 and ASTM D3574 methodology, and automatically reports thickness and firmness loss. Because we design and manufacture the device in Türkiye, our Izmir-based team provides on-site, fast solutions whenever you need calibration, software updates, or technical support; you won’t be stuck with the weeks-long service process of imported devices.