How Silicone Performs Under Pressure
Rubber components, such as compression seals, gaskets and cushioning parts, must perform reliably under long-term stress. At Silicone Engineering, we understand the importance of selecting materials that not only meet performance requirements today but continue delivering over the lifespan of the product. That’s why we focus heavily on mechanical tests like compression set and stress relaxation to help engineers, designers and procurement professionals choose with confidence.
These mechanical tests tell us how an elastomer behaves under load or strain over time, which directly relates to how well it can seal, cushion or maintain force. In this short guide, we explore the most critical performance factors for silicone-based materials, and how we test them at Silicone Engineering.
Compression Set
Compression set is a crucial performance metric for elastomers, particularly in applications that require long-term sealing or load retention. A lower compression set indicates better recovery properties, which is vital for a range of components from gaskets and O-rings to enclosure seals.
‘Compression set’ refers to the permanent deformation that remains in a material after it has been compressed under a constant strain and then released. The test records the percentage of lost thickness, with lower percentages equalling better material recovery.
For instance, a silicone gasket used in a high-temperature environment, like an engine compartment or power enclosure, may gradually lose its ability to maintain a tight seal if it suffers from a high compression set. Even a small change in shape could compromise sealing force and allow for leaks, vibrations or ingress.
At Silicone Engineering, we design and formulate silicone sponge and solid rubber grades to consistently achieve industry-standards, depending on grade and intended use.
Stress Relaxation
Stress relaxation testing measures how much force is lost over time when a rubber material is held in a compressed state. While the shape of the material may appear unchanged, the internal stress or “pushback” reduces as molecular chains move and adjust.
This loss of force can be critical in long-term sealing applications like enclosure gaskets, O-rings and pressure-sensitive components. If the seal force weakens too much, even without visible deformation, the product can fail.
To test stress relaxation, the rubber is compressed to a fixed deflection and the retained force is measured at intervals. The result is expressed as a percentage force lost over time. A material with slower relaxation retains its sealing force longer.
🔬 How We Test Silicone: Compression Force Deflection (CFD)
While this blog focuses on long-term performance, it’s equally important to understand how a material behaves under initial compression. That’s where Compression Force Deflection (CFD) testing comes in.
At Silicone Engineering, we carry out CFD testing in-house using equipment that complies with ASTM D1056. This test tells us how much force is required to compress a material by a specific percentage, most commonly 25%. It’s particularly relevant for engineers choosing materials for cushioning, gasketing or vibration control, where both flexibility and resilience are important.
Seeing how our silicone sponge materials respond under load provides confidence in their suitability for real-world applications. The data generated from CFD testing is used in conjunction with compression set and stress relaxation results to guide material selection and formulation.
| Condition | What’s Constant | What Changes Over Time | Failure Risk |
|---|---|---|---|
| Compression Set | Deflected, then released | Deflection | Permanent deformation – loss of shape/seal |
| Stress Relaxation | Constant deflection | Deformation (force) | Loss of sealing force |
Ask the Right Questions
At Silicone Engineering, we believe that great product performance starts with asking the right questions. Compression set and stress relaxation may sound similar, but they measure different failure modes, and both are essential for long-lasting silicone solutions.
Rather than focusing solely on colour, hardness or thickness, it’s critical to understand how a material performs under strain and over time. With rigorous in-house testing and formulation expertise, we help engineers and designers make informed choices for better outcomes, fewer failures, and longer-lasting components.
For all your silicone requirements, get in touch with our team of specialists today.