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.
Precise, repeatable fatigue testing with Vilutra
14 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.