Compression Set in Elastomers: How It Happens and How to Prevent It

In the world of sealing technology, compression set is one of the most common, and preventable, failure modes in elastomeric seals. Whether you’re using O-rings, gaskets, or custom rubber parts, understanding compression set and how to mitigate it is crucial for reliable, long-term performance.

In this expanded guide, we’ll explore what compression set is, why it happens, how it affects sealing performance, how it’s measured, and the strategies you can use to prevent it. We’ll also explain how Canyon Components helps customers choose materials and designs that minimize this issue.

What Is Compression Set?

Compression set is the permanent deformation of an elastomer after it has been compressed and released. In sealing applications, elastomers are compressed to create a tight seal between two surfaces. Ideally, when the pressure is released, the elastomer should return to its original shape. But over time, materials can lose their ability to rebound.

When this happens, the seal loses contact pressure, which can result in leaks, even if the material hasn’t cracked or worn through.

Compression set is usually measured as a percentage, calculated by comparing the thickness of the material before compression, the thickness after compression for a defined period, and the thickness after recovery.

How Compression Set is Determined

Compression set is generally determined through air aging tests and reported as the percent of deflection by which the elastomer fails to recover after a fixed time under a specified squeeze and temperature.

• 0% compression set means no relaxation has occurred; the material has fully recovered.
• 100% compression set indicates total relaxation; the seal may still contact the mating surfaces but exerts no force against them.

Compression set can also be expressed as a percentage of the original thickness, but percent of original deflection is the more common measurement in the sealing industry.

Measuring Compression Set

Standards such as ASTM D395 define procedures for measuring compression set:

• Method A: Compression between plates
• Method B: Compression using a compression device (common for O-rings)

Results are typically reported as a percentage; lower percentages indicate better resistance to compression set.

Balancing Compression Set with Other Properties

While low compression set values are generally desirable, real-world sealing performance depends on more than just this number. Seal designers must weigh compression set resistance alongside other critical properties such as chemical compatibility, tensile strength, tear resistance, and temperature range. Overemphasizing one property can lead to suboptimal performance.

This is the eternal sealing compromise; selecting a material that balances all properties for the intended service conditions.

When High Compression Set Doesn’t Mean Failure

From a theoretical standpoint, high compression set might seem like a recipe for seal failure. In practice, a seal can sometimes continue to function even after taking a 100% compression set, provided:

• System temperature and pressure remain stable
• There is no motion or vibration to disturb the sealing interface
• The seal remains in uninterrupted contact with the mating surfaces

In certain situations, fluid swell can actually compensate for compression set. If the service fluid causes the elastomer to expand, the additional volume can help maintain sealing force despite a loss in elastic recovery.

How Fluid Interaction Affects Compression Set

Laboratory tests illustrate how fluid interaction can dramatically change compression set results:

• In air and in a fluid that caused slight shrinkage, a compound showed ~20–25% compression set.
• In a fluid that caused a 20% swell, there was no measurable compression set.

The most dangerous scenario is high compression set combined with shrinkage. When this happens, the seal loses contact pressure and physical dimensions simultaneously, almost guaranteeing leakage unless exceptionally high squeeze is designed into the gland.

Causes of Compression Set

Several factors contribute to compression set in elastomers:

• Temperature: High temperatures accelerate chemical changes in elastomers, including crosslink breakdown or reformation.
• Compression force and time: Greater squeeze and longer duration increase the likelihood of permanent deformation.
• Material choice: Different elastomers have varying inherent resistance to compression set.
• Chemical exposure: Fluids can extract plasticizers or cause swelling, altering material structure.
• Improper installation: Nicks, twists, or uneven compression create localized stresses.
• Environmental factors: UV, ozone, and humidity can age elastomers and reduce rebound characteristics.

Industry-Specific Impact

• Aerospace: High compression set in hydraulic or fuel seals can cause critical failures.
• Food & Beverage: Seals in CIP systems face constant compression, heat, and chemicals.
• Oil & Gas: Downhole seals need extreme resistance to compression set to withstand high pressures and temperatures.

How to Prevent Compression Set

Choose the Right Material

Match elastomer capabilities to your operating conditions:

• EPDM: Excellent for steam and hot water, good compression set resistance at moderate temperatures.
• FKM: FKM materials, like Viton™, have good high-temperature performance and chemical resistance.
• FFKM: FFKM materials, like Kalrez®, Canrez®, or Chemraz®, exhibit exceptional high-temperature and chemical resistance.
• HNBR: Strong mechanical properties for oil applications.

Optimize Seal Design

• Avoid over-compression.
• Design for even loading.
• Consider differences in dynamic vs. static seals.
• Learn more about optimal design at our Reference Hub.

Control Operating Conditions

• Limit exposure to maximum rated temperatures.
• Reduce dwell time under compression.
• Avoid unnecessary preload during storage.
• Learn more about optimal design at our Reference Hub.

Proper Installation and Handling

• Lubricate seals appropriately.
• Keep surfaces clean and smooth.
• Use proper tools to avoid damage.
• Learn more about optimal design at our Reference Hub.

Maintenance and Inspection

• Replace seals at recommended intervals.
• Monitor for early leakage.
• Track seal performance over time.
• Learn more about optimal design at our Reference Hub.

Canyon Components’ Approach

We:

• Review application details to recommend optimal materials.
• Provide samples for in-field or lab testing.
• Offer custom compounds engineered for compression set resistance.
• Supply detailed technical data and ASTM test results.
• Talk with the Canyon Components Engineering Team now!

Real-World Example

A pharmaceutical customer experienced seal failures in steam sterilization. Their silicone gaskets showed 70% compression set after three months. We recommended a platinum-cured, high temperature silicone with enhanced compression set resistance, doubling service life and reducing downtime.

Conclusion

Compression set is a common cause of seal failure, but with proper material selection, design, and operating practices, it can be significantly reduced. Understanding the causes, testing under relevant conditions, and accounting for factors like swell and shrinkage are key to long-term seal performance.

Whether you need an aerospace O-ring, a compliant gasket for food processing, or a chemical-resistant seal, Canyon Components can help you select a solution that minimizes compression set and maximizes performance.