Rebound Rate Test Specifications: Standards, Methods, and Applications

Rebound rate (resilience) testing quantifies the energy a material returns after an impact, and it serves as a critical quality and performance indicator for rubber, elastomers, flexible foams, and sealing materials. This article summarizes the international and national test specifications governing rebound rate measurement, covering specimen requirements, apparatus, test procedures, calculations, and typical industrial applications. Whether you are benchmarking high-resilience polyurethane foam or qualifying gasket recovery, this guide explains how accredited third-party laboratories apply the relevant ISO, ASTM, EN, and GB standards.

Technical Overview

The rebound rate, also referred to as rebound resilience, is the percentage of mechanically applied energy that a material returns after being struck or compressed and released. In practice, it is calculated as the ratio of the rebound height (or rebound energy) of a falling body, ball, or pendulum to its initial drop height (or impact energy), expressed as a percentage. A higher rebound rate indicates a more elastic material, while a lower value indicates greater energy absorption through viscous or plastic deformation.

Rebound rate test specifications are standardized by recognized standards organizations. For rubber and elastomeric materials, the principal methods include ISO 4662, ASTM D2632, ASTM D7121, DIN 53512, and GB/T 1681. For flexible cellular materials such as polyurethane foam, ball rebound resilience is determined in accordance with ASTM D3574 (Test H), ISO 8307, and GB/T 10652. For gasket and sealing materials, compressibility and recovery are evaluated using ASTM F36. Because rebound rate is sensitive to temperature, specimen geometry, and aging history, strict adherence to the specified conditioning and test conditions is essential for reproducible results.

Testing Samples

Rubber and Elastomer Test Pieces

Vulcanized rubber and thermoplastic elastomer samples are typically prepared as cylindrical discs, commonly on the order of 29 mm in diameter and 12.5 mm in thickness, or as alternative geometries permitted by the applicable standard. Specimens must be flat, parallel-sided, and free from voids, blisters, and surface defects. Finished components such as bushings, mounts, rollers, and O-rings can be tested by cutting representative sections, provided the test surface is supported on a rigid anvil.

Flexible Cellular Foam Blocks

For ball rebound testing of polyurethane, latex, and other flexible foams, specimens are generally cut as blocks of at least 100 mm × 100 mm in area with a thickness of approximately 50 mm. Testing is normally performed in the direction of foam rise, since cellular materials are anisotropic and show different resilience values along different axes. Skins, densified layers, and adhered coverings should be removed before testing.

Gasket and Sealing Material Specimens

Gasket materials, including compressed fiber sheets, PTFE-based composites, graphite laminates, and rubber sheeting, are tested as conditioned specimen stacks or strips with parallel surfaces. The recovery (rebound) of the material is measured after a defined compressive loading cycle that simulates flange tightening conditions.

Environmental and Aged Specimens

To assess service performance, specimens may be conditioned at elevated temperatures, low temperatures, or after heat, oil, or ozone aging before rebound measurement. Low-temperature rebound testing is particularly important for seals, footwear, and outdoor components that must remain elastic in cold climates.

Testing Items

Common test items conducted under rebound rate specifications include:

• Vertical rebound resilience of rubber by falling-plunger (resiliometer) method in accordance with ASTM D2632
• Pendulum (Schob-type) rebound resilience of vulcanized or thermoplastic rubber in accordance with ISO 4662, ASTM D7121, and DIN 53512
• Ball rebound resilience of flexible cellular materials in accordance with ASTM D3574 (Test H), ISO 8307, and GB/T 10652
• Rebound resilience of rubber at ambient, low, and elevated temperatures
• Compressibility and recovery of gasket materials in accordance with ASTM F36
• Resilience retention after thermal, oxidative, or fluid aging exposures

Testing Methods

Specimen Conditioning

All specimens are conditioned in a controlled atmosphere, typically 23 ± 2 °C and 50 ± 5 % relative humidity, for a minimum of 16 hours prior to testing, in line with general rubber test practice such as ISO 23529. Testing is performed at the same standard laboratory temperature unless a specific service temperature is specified, in which case the specimen is held at temperature until thermal equilibrium is reached.

Vertical Rebound (Falling Body) Method

In the falling-body method described by ASTM D2632, a weighted plunger is dropped from a fixed height onto the horizontal test surface. The rebound height of the plunger is read against a calibrated graduated scale, and the rebound rate is calculated as the rebound height divided by the drop height, multiplied by 100. The apparatus is leveled so that the impact is normal to the specimen surface, and the specimen rests on a rigid, massive base.

Pendulum Rebound Method

In the pendulum method of ISO 4662, ASTM D7121, DIN 53512, and GB/T 1681, a pendulum hammer of defined geometry and impact energy strikes the clamped specimen. The angle or height reached on the return swing is measured, and the resilience is expressed as the ratio of returned energy to impact energy. The pendulum method is well suited to comparative material ranking and quality control because it delivers a controlled, repeatable impact velocity.

Ball Rebound Method for Foams

In ball rebound testing per ASTM D3574 (Test H) and ISO 8307, a polished steel ball, typically 16 mm in diameter, is dropped from a fixed height of approximately 500 mm onto the foam specimen. The maximum rebound height is observed with a mirror scale or optical sensor, and resilience is reported as the rebound height divided by the drop height, expressed as a percentage. Foams exhibiting ball rebound values above roughly 45–50 % are commonly classified as high-resilience grades.

Gasket Recovery Method

In the gasket recovery test of ASTM F36, the conditioned specimen is compressed between parallel platens at a specified pressure for a defined holding period. Thickness is measured before loading, under load, and after load release. Compressibility and recovery percentages are calculated from these thickness readings, quantifying the material's ability to rebound and maintain sealing stress.

Calculation and Reporting

The rebound rate is calculated as: R = (h2 / h1) × 100 %, where h1 is the initial drop height and h2 is the rebound height. A minimum of three specimens or measurement points is normally tested, and the median or mean value is reported as specified by the method. The test report should identify the standard used, material designation, specimen dimensions and orientation, conditioning and test temperature, individual and reported rebound values, and any deviations from the standard.

Applications

Rebound rate testing is applied across a wide range of industries:

• Automotive: engine mounts, suspension bushings, seals, tires, seating foam, and interior padding
• Footwear: midsole and insole cushioning materials for energy return and comfort
• Furniture and bedding: polyurethane and latex foams graded for resilience and durability
• Industrial sealing: flange gaskets, pipe seals, and door seals where recovery maintains leak-tightness
• Sports and recreation: running tracks, playground surfaces, gym flooring, and protective padding
• Building materials: vibration isolation pads, expansion joint fillers, and acoustic underlays
• Electronics: thermal interface pads and enclosure gaskets requiring controlled compression recovery

It should be noted that concrete rebound hammer testing, governed by ASTM C805, EN 12504-2, and JGJ/T 23, is a distinct technique that measures a rebound number to estimate in-place compressive strength, and it should not be confused with material rebound resilience testing.

FAQ

What is the difference between rebound rate and compression set?

Rebound rate measures the instantaneous elastic energy return of a material after impact, while compression set measures the permanent deformation remaining after a sustained compression. A material can exhibit high rebound resilience yet still show unacceptable compression set after long-term loading, so the two properties are evaluated separately depending on the application.

Which standard should be selected for flexible polyurethane foam?

For flexible cellular materials, ball rebound resilience is normally tested in accordance with ASTM D3574 (Test H) or ISO 8307, with GB/T 10652 serving as the corresponding national method. For dense rubbers and elastomers, ISO 4662, ASTM D2632, or GB/T 1681 are the appropriate specifications.

Why do foam test results differ with specimen orientation?

Flexible foams are anisotropic because cell structures elongate in the rise direction during manufacturing. Testing perpendicular to the rise direction is specified in most standards, so laboratories must record orientation and always compare results measured in the same direction.

How does temperature affect rebound rate results?

Rebound rate decreases significantly as materials approach their glass transition temperature and may increase with temperature as viscous losses decline. Specifications therefore define conditioning and test temperatures precisely, and low-temperature rebound testing is recommended for components used in cold environments.

What is a typical acceptance criterion?

Acceptance values depend entirely on the product specification. Conventional flexible polyurethane foams commonly fall in the range of 30–50 % ball rebound, high-resilience foams exceed about 55 %, and many engineering rubber compounds fall between 20 % and 70 % depending on formulation and hardness. Contract documents or purchase specifications should always state the required minimum and the governing test standard.

Can finished parts be tested instead of molded test plaques?

Yes, provided a representative flat test area of sufficient thickness and support can be obtained. Results from finished parts may differ from molded plaques due to processing, curing, and thickness effects, so the sampling location should be documented and agreed between the parties in advance.