For manufacturers and engineers, the performance of elastomeric materials is often defined by their ability to recover from deformation. A key metric in this evaluation is compression set. Understanding and controlling compression set is critical for ensuring the long-term reliability and function of seals, gaskets, and other elastomeric components in products ranging from automotive engines to medical devices. When a material fails to recover its original shape, its ability to perform its sealing function is compromised, leading to leaks and product failure.

This guide provides a professional overview of compression set, exploring its causes, how it’s measured, and offering actionable strategies to mitigate its effects.

What is Compression Set?

Compression set is the permanent deformation that remains in a material after it has been subjected to a constant compressive force for a period of time and at a specific temperature. Imagine a rubber gasket that has been squeezed between two flanges for months. When the flanges are separated, if the gasket doesn’t return to its original thickness, the portion of that deformation that remains is the compression set. This permanent deformation is expressed as a percentage of the original deflection. A low compression set percentage is desirable, as it indicates the material has retained its elastic properties and will continue to perform its sealing function effectively.

Factors Influencing Compression Set

The degree of compression set is not an inherent property of a material but is influenced by several key factors:

• Material Chemistry: The polymer’s base chemistry plays a major role. For example, materials like silicone and fluoroelastomers are known for having very low compression set, making them ideal for high-performance sealing applications. In contrast, general-purpose rubbers may have a higher compression set.
• Temperature: Higher temperatures accelerate the chemical processes that cause permanent deformation. A material’s compression set is always tested at a specific temperature, as its performance will be significantly different at room temperature versus an elevated temperature.
• Time: The duration of the compressive force is a critical factor. The longer a material is under compression, the greater the compression set will be. This is why long-term sealing applications require materials with very low compression set.
• Cure and Compound Formulation: The curing process and the specific additives used in the elastomer compound can be adjusted to optimize compression set. A well-cured material is less likely to undergo permanent deformation.

Measuring Compression Set: An Industry Standard

Compression set is measured according to industry standards, most commonly ASTM D395. The standard procedure involves compressing a test specimen to a specific deflection (typically 25%) and holding it for a set time and temperature. After the specified time, the force is removed, and the specimen is allowed to recover for a short period. The percentage of compression set is then calculated as the ratio of the permanent deformation to the original deflection. A value of 0% indicates perfect recovery, while 100% indicates the material has completely lost its elasticity and retained all of the deformation.

Actionable Advice for Professionals

To ensure your elastomeric components perform reliably, consider these strategies:

1. Specify by Application: Do not choose a material based on a generic “good for sealing” claim. Specify your material based on its compression set data for the exact temperature and duration it will be exposed to in its end-use environment.
2. Look for Low Compression Set Ratings: When evaluating materials for seals and gaskets, prioritize those with low compression set percentages. These materials will maintain their sealing force longer, preventing leaks and premature failure.
3. Consider a Proper Cure: A post-cure process can significantly improve a material’s compression set performance. Work with your material supplier to ensure the elastomer compound is fully cured to achieve its maximum performance.
4. Partner with a Material Specialist: The best way to ensure you’re using the right material is to work with a supplier who understands the nuances of elastomer chemistry. A specialist can help you select a compound that is formulated to resist compression set under your specific operating conditions.

Incure: Your Partner in High-Performance Materials

At Incure, we understand the critical role that material performance plays in product success. We specialize in providing a portfolio of high-performance elastomeric materials, including advanced thermoplastic elastomers (TPEs), that are engineered for low compression set and superior durability. Our team of technical specialists is dedicated to collaborating with you, helping you navigate the complexities of material selection and ensuring you choose a solution that will fortify your products against the challenges of time and temperature. Partner with Incure to build a foundation of quality and trust in every component you design.