Elastomer Compression and Rebound Resilience Testing: Standards, Methods, and Applications

Elastomer compression and rebound resilience testing measures the ability of rubber and elastomeric materials to recover their original thickness and return energy after a compressive load is applied and removed, providing critical data for sealing performance, cushioning efficiency, and long-term reliability. Conducted in accordance with international standards such as ISO 815, ASTM D395, ASTM F36, and ISO 4662, these tests are essential for evaluating gaskets, O-rings, foam seals, and rubber components across automotive, construction, and industrial applications. This guide explains the test principles, sample requirements, testing methods, typical parameters, and common acceptance criteria for compression and rebound testing of elastomers.

Technical Overview

Elastomer compression and rebound rate testing evaluates two related but distinct performance characteristics: the dimensional recovery behavior after sustained compression (compression set and compressibility-recovery) and the energy-return capability under dynamic impact (rebound resilience). Together, these properties determine whether a seal will maintain adequate contact pressure over years of service and how efficiently an elastomer absorbs and returns mechanical energy during loading cycles.

The compression rebound rate is generally expressed as the percentage of thickness or deflection recovered after a defined compression cycle. A high rebound rate indicates low permanent deformation, strong sealing-force retention, and durable cushioning performance, while a low value may signal material degradation, over-compression, chemical attack, or poor low-temperature flexibility.

Because results are highly sensitive to temperature, time, strain level, and cure state, tests are performed under tightly controlled laboratory conditions, typically at 23 °C ± 2 °C and 50 % ± 5 % relative humidity, using calibrated compression fixtures, thermostatic ovens, and precision thickness gauges in accredited third-party laboratories. The governing reference standards include ISO 815-1/815-2, ASTM D395, ASTM F36, ASTM D575, ISO 4662, ISO 3384, and their GB/T and JIS equivalents such as GB/T 7759, GB/T 1681, JIS K 6262, and JIS K 6255.

Testing Samples

Vulcanized Rubber Specimens

Standard cylindrical test buttons molded from compounds such as NR, SBR, NBR, EPDM, FKM, and silicone (VMQ). ASTM D395 specifies specimens of 29.0 mm diameter and 12.5 mm thickness, while ISO 815-1 Type A specifies 13.0 mm diameter and 6.3 mm thickness. Specimens must be fully cured, free of porosity, blisters, and surface defects, with parallel faces.

Thermoplastic Elastomers

TPE, TPV, TPU, and TPO compounds used for automotive glass runs, soft-touch grips, and dynamic seals. Test buttons are typically injection molded or die-cut from compression-molded plaques, with grain orientation recorded when anisotropy is expected.

Cellular and Sponge Elastomers

Closed-cell and open-cell materials such as EPDM sponge profiles, CR foam, and polyurethane foam gaskets. Larger specimens are tested in accordance with ASTM D3574 or ISO 7214, and thickness must be measured with a low-pressure dial gauge to avoid artificially compressing the cellular structure.

Finished Products and Gasket Materials

O-rings, flange gaskets, door and window sealing profiles, battery sealing pads, and cabinet gaskets. Actual parts may be tested as received in dedicated fixtures, or representative material plaques may be evaluated under ASTM F36 for compressibility and recovery.

Testing Items

• Compression set under constant deflection (Method B) and under constant load (Method A)
• Compressibility and recovery of gasket sheet materials
• Rebound resilience by pendulum and vertical rebound methods
• Compression deflection and stress-strain characteristics of rubber in compression
• Compression stress relaxation at constant deflection for sealing force retention
• Low-temperature compression set and temperature retraction behavior
• Cyclic compression fatigue and dynamic recovery evaluation for cushioning materials

Testing Methods

Compression Set Testing (ISO 815-1, ASTM D395, GB/T 7759)

Specimens are compressed between parallel platens, either to 25 % deflection using rigid spacers (constant deflection method) or under a fixed load (constant load method). The assembly is placed in a circulating-air oven for a defined period, commonly 22 h, 70 h, or 168 h, at temperatures ranging from 23 °C up to 250 °C depending on the polymer class. After release, the specimen recovers for 30 minutes at laboratory temperature before final thickness is measured. Compression set is calculated as CB = (t0 − t1) / (t0 − ts) × 100 %, where t0 is the original thickness, t1 is the recovered thickness, and ts is the spacer thickness. The compression rebound rate is correspondingly reported as 100 − CB.

Compressibility and Recovery of Gasket Materials (ASTM F36)

A specimen is loaded to a ram pressure of approximately 34.5 MPa. Compressibility is calculated as the reduction in thickness under load divided by the original thickness, expressed as a percentage. Recovery is calculated as the thickness regained after the load is removed divided by the total deflection under load, expressed as a percentage. Higher recovery values indicate that the gasket can compensate for flange movement, thermal cycling, and relaxation of bolts over time.

Rebound Resilience Testing (ISO 4662, ASTM D2632, GB/T 1681, JIS K 6255)

In the pendulum method, a pendulum hammer of defined mass and impact velocity strikes a clamped test piece, and the ratio of returned energy to input energy is recorded as resilience in percent. In the vertical rebound method, a weighted striker is dropped from a fixed height onto the specimen, and resilience is calculated as the rebound height divided by the drop height, multiplied by 100. Resilience data are used to grade materials for vibration damping, anti-vibration mounts, and impact absorption where energy return must be maximized or deliberately minimized.

Compression Deflection and Stress Relaxation

Compression deflection testing per ASTM D575 measures the load required to produce a given deflection, or the deflection produced by a given load, generating force-deflection curves for spring-rate design. Stress relaxation testing per ISO 3384 holds a specimen at constant deflection and monitors the decay of counterforce over time, which is a direct indicator of long-term sealing pressure retention in static seals.

Low-Temperature Recovery Testing

ISO 815-2 determines compression set at subzero temperatures down to −80 °C, and temperature retraction testing per ASTM D1329 (TR 10, TR 30, TR 50, TR 70) characterizes the recovery of a stretched and frozen specimen as it warms. These methods are critical for outdoor, automotive cold-crank, and cryogenic sealing applications.

Applications

• Automotive sealing systems: door and window seals, hood gaskets, trunk seals, lamp seals, and battery pack sealing for electric vehicles
• Industrial hydraulics and pneumatics: O-rings, rod and piston seals, valve seats, and diaphragms requiring low compression set
• Pipe flanges and pressure equipment: elastomeric and composite gaskets qualified for compressibility and recovery performance
• Building and construction: curtain wall gaskets, expansion joint fillers, and weather-stripping profiles exposed to long-term compression and weathering
• Rail transit and heavy machinery: resilient pads, axle bushings, cone buffers, and anti-vibration components requiring controlled resilience
• Electronics and appliances: foam enclosure gaskets, display sealing cushions, and EMC shielding foams with defined compression-recovery behavior
• Medical and analytical devices: stoppers, syringe seals, and instrument gaskets demanding reliable recovery after sterilization

FAQ

What is the difference between compression set and compression rebound rate?

Compression set quantifies the permanent deformation that remains after a specimen is compressed and released, expressed as a percentage of the applied deflection. The compression rebound rate is effectively its complement, describing the portion of the deformation that was recovered. Rebound resilience under ISO 4662 and ASTM D2632 is a separate dynamic property that measures energy return during a rapid impact rather than dimensional recovery after sustained compression.

What temperatures and durations are typically used for compression set testing?

Common conditions include 70 °C or 100 °C for 22 h or 70 h in accordance with ASTM D395 and ISO 815-1. Heat-resistant polymers such as silicone and FKM are frequently evaluated at 150 °C to 250 °C, while low-temperature grades are tested at −10 °C to −40 °C under ISO 815-2. Test conditions should always reflect the actual service environment of the component.

What sample dimensions and quantities are required?

A minimum of three specimens is recommended for statistical validity. Standard ASTM D395 buttons measure 29.0 mm × 12.5 mm, and ISO 815-1 Type A buttons measure 13.0 mm × 6.3 mm. Finished parts such as O-rings and profiles can be tested as received using appropriate fixtures, provided the geometry is documented.

What is considered an acceptable compression rebound result?

Acceptance criteria are defined in each material or product specification, but typical engineering seals require a compression set below 10 % to 20 % after 22 h at 100 °C, equivalent to a rebound rate above 80 % to 90 %. For gasket materials under ASTM F36, recovery values of 35 % to 90 % are common depending on the material class and application.

Can finished seals and assemblies be tested instead of molded buttons?

Yes. Testing actual parts provides the most realistic assessment of performance, since geometry, surface treatment, and processing history all influence recovery behavior. Results on finished parts should be interpreted with the understanding that non-standard geometries may not be directly comparable to data from standard specimens.

How long does compression and rebound testing take?

A standard 22 h compression set cycle plus conditioning and measurement is typically completed within a few working days. Extended 70 h or 168 h exposures, multiple temperature points, stress relaxation programs of 1000 h or longer, and low-temperature recovery tests extend the schedule accordingly, with typical project turnaround of five to fifteen working days in accredited third-party laboratories.