Why It Matters

Polyurethane’s compression set is an important property to consider when your component must endure a compressive load. Examples of applications include bumpers, equipment mounts, vibration isolation pads, and rollers. Urethane’s compression set indicates how well the polyurethane will retain its elastic properties under compression.

A compound with low compression set will recover quite well, even if maintained in a compressed state for an extended period of time. Conversely, a compound with a high compression set will not recover as well. It will permanently retain much more of the deflection upon removal of the compressive stress.

Polyurethane’s compression set depends on a combination of basic properties such as modulus and the degree of molecular cross-linking, which result from the polyurethane’s formulation. We can tailor the polyurethane’s resistance to compression set to fit your specific need.

Measurement

• Constant Force, sometimes referred to as Method A. This test compresses a test specimen between parallel rigid plates under a constant stress. Then compression set is calculated as a percentage of the specimen’s permanent deformation to its original thickness.
• Constant Deflection, sometimes referred to as Method B. This test compresses a test specimen between parallel rigid plates to 75% of its original thickness. Then compression set is calculated as a percentage of the specimen’s permanent deformation to the applied deflection.

Typical Values

The lowest compression set is achieved with highly cross-linked urethanes.

Polyurethane’s compression set typically ranges from 5-40%.