Rebound resilience testing technology quantifies the ability of rubber, elastomers, and flexible foam materials to return impact energy, making it one of the most important indicators of elastic performance in material design and quality control. This technical guide explains the testing principles, internationally recognized standards such as ISO 4662, ISO 8307, and ASTM D3574, sample requirements, core testing methods, and typical industry applications, helping manufacturers select the most suitable rebound rate test for their products.
Technical Overview
Rebound rate, commonly referred to as rebound resilience, is defined as the percentage of mechanical energy that a material returns after being deformed by an impacting body, expressed relative to the initial impact energy. It is a fundamental dynamic property of elastomeric and cellular materials, reflecting the balance between elastic energy storage and viscous energy dissipation within the polymer structure.
From a materials science perspective, rebound resilience is closely linked to the viscoelastic character of the polymer network. Materials with a dominant elastic response return most of the impact energy and exhibit high resilience, while viscous or highly damped materials absorb energy as heat and show low resilience. For this reason, rebound rate testing is widely used to evaluate hysteresis loss, damping behavior, fatigue tendency, and the dynamic comfort or energy-return performance of finished products.
Testing is governed by internationally recognized standards, including ISO 4662 and ASTM D2632 for vulcanized and thermoplastic rubber, ISO 8307 and ASTM D3574 (Test H) for flexible cellular polymeric materials, and the corresponding national methods GB/T 1681 and GB/T 6670. Accredited third-party laboratories routinely perform these tests for material qualification, supplier comparison, and regulatory compliance across the rubber, foam, footwear, automotive, and sports industries.
Testing Samples
Vulcanized Rubber and Thermoplastic Elastomers
Compact elastomeric materials such as vulcanized natural rubber, SBR, NBR, EPDM compounds, silicone rubber, and thermoplastic elastomers (TPO, TPU, TPE) are tested in the form of flat molded sheets or standard test pieces with smooth, parallel surfaces. Typical specimen thicknesses range from approximately 4 mm to 15 mm, depending on the selected standard and test method.
Flexible Polyurethane Foams
Slabstock and molded flexible polyurethane foams, including high-resilience (HR) grades and viscoelastic (memory) foams, are core test materials for ball rebound evaluation. Specimens generally require a minimum thickness of about 50 mm, which may be achieved by stacking parallel-cut layers when the product is thinner. The foam cell structure, density, and orientation significantly influence the measured result.
Polyolefin and Specialty Foams
Closed-cell and cross-linked foams such as EVA, PE, PP blends, and rubber-modified foams used in midsoles, mats, and packaging can also be characterized. Because these materials show pronounced thickness and density effects, specimens must be prepared with uniform cell structure and clearly documented thickness.
Finished Products and Components
Finished or semi-finished articles such as shoe midsoles and insoles, sealing strips, gaskets, anti-vibration pads, sports mats, and cushioning layers may be tested directly when a suitable flat test area is available. Testing on actual products provides the most realistic assessment of end-use energy return and cushioning performance.
Regardless of material type, proper specimen conditioning is essential for reproducible results. Key conditioning requirements include:
- Conditioning at a standard laboratory atmosphere of 23 ± 2 °C and 50 ± 5% relative humidity for a minimum of 16 hours, or as specified by the applicable standard.
- Flat, parallel upper and lower surfaces, free of skin defects, voids, and visible cell damage.
- Specimen dimensions and thickness compliant with the requirements of the selected test method.
- Avoidance of testing within edge zones or areas affected by cutting and molding.
Testing Items
Rebound rate testing covers a range of measurable parameters that characterize the elastic energy return of a material under standardized impact conditions. Common testing items include:
- Ball rebound resilience of flexible cellular materials per ISO 8307, ASTM D3574 Test H, and GB/T 6670.
- Schob pendulum rebound resilience of vulcanized or thermoplastic rubber per ISO 4662 and GB/T 1681.
- Vertical rebound resilience of rubber per ASTM D2632.
- Rebound resilience at elevated or reduced temperatures to evaluate thermal dependence.
- Resilience retention after thermal aging, humidity exposure, compression fatigue, or flexing cycles.
- Comparative resilience mapping across different material batches, densities, or formulations.
Testing Methods
Ball Rebound Test (Free-Falling Ball Method)
In the ball rebound method, a polished steel ball of specified mass, typically around 16 g, is released from a fixed drop height, commonly 500 mm, onto the horizontal surface of the specimen. The maximum rebound height is captured using optical, infrared, or video-based sensors, and the rebound resilience is calculated as R (%) = (h2 / h1) × 100, where h1 is the drop height and h2 is the rebound height. This method is the reference procedure for flexible polyurethane and polyolefin foams and directly reflects the cushioning and energy-return behavior perceived in seating, bedding, and footwear applications.
Schob Pendulum Test
The Schob pendulum method uses a pendulum-mounted striker of defined mass and geometry that is released from a fixed starting angle and impacts the clamped specimen at a controlled velocity of approximately 2 m/s. The rebound height or return angle of the pendulum is measured, and resilience is computed from the ratio of rebound energy to impact energy. This method is the standard approach for compact vulcanized rubbers and thermoplastic elastomers under ISO 4662 and GB/T 1681, offering high repeatability and low specimen consumption.
Vertical Rebound Resiliometer Method
The vertical rebound resiliometer described in ASTM D2632 employs a guided plunger of specified mass that falls vertically onto the specimen. The rebound distance is read directly as a percentage resilience on a graduated scale. The instrument is compact and fast, making it popular for in-process quality control and rapid comparative screening of rubber compounds.
Test Procedure and Data Evaluation
A typical rebound resilience test follows a standardized sequence: specimen conditioning, dimensional measurement, instrument calibration, execution of impacts at several well-spaced points on the specimen, and statistical evaluation of the results. Depending on the standard, the first impact may be discarded as a conditioning drop, and the reported value is calculated as the mean or median of the remaining readings. Test reports should clearly state the applied standard, specimen thickness, conditioning history, test temperature, and individual measured values.
Several factors must be controlled because they strongly influence rebound results:
- Test temperature and relative humidity, since resilience of most elastomers increases with temperature.
- Specimen thickness, density, and cellular structure, particularly for foamed materials.
- Ball mass, drop height, or pendulum energy, which must match the specified standard parameters.
- Surface flatness and clamping condition of the specimen.
- Degree of vulcanization or crosslinking and the filler content of the compound.
- Aging, fatigue, or compression history prior to testing.
Applications
Rebound rate testing supports product development, material selection, incoming material inspection, and lot release testing across a broad range of industries. Typical application areas include:
- Footwear: evaluation of midsole and insole energy return, cushioning comfort, and fatigue resistance for running shoes and athletic footwear.
- Automotive: characterization of seating foams, sealing systems, bushings, engine mounts, and NVH components.
- Sports and leisure: performance assessment of sports balls, gym mats, playground surfaces, and flooring systems.
- Packaging and logistics: selection of cushioning foams with appropriate energy absorption and recovery behavior for protective packaging.
- Furniture and bedding: comfort grading of flexible foams for mattresses, pillows, and upholstered products.
- Industrial rubber products: quality control of anti-vibration pads, rollers, belts, and damping elements.
- Research and development: comparison of polymer formulations, blowing systems, and crosslinking technologies.
By correlating rebound resilience data with density, hardness, compression set, and fatigue results, engineers can build a complete dynamic performance profile of a material and reliably predict its behavior in real service conditions.
FAQ
What is the difference between ball rebound and pendulum rebound testing?
Ball rebound testing drops a steel ball onto the specimen from a fixed height and measures the rebound height, and it is primarily used for flexible cellular foams. Pendulum testing, such as the Schob method, strikes the specimen with a swinging hammer and measures the rebound of the pendulum, and it is mainly used for compact vulcanized rubbers and thermoplastic elastomers. The two methods produce different numeric values for the same material, so results must only be compared within the same method and standard.
What sample thickness is required for rebound testing?
For ball rebound tests on flexible foam, a minimum specimen thickness of approximately 50 mm is generally required, and thinner products may be tested by stacking layers. For pendulum and vertical rebound tests on compact rubber, standard thicknesses are typically in the range of a few millimeters to about 15 mm. The exact requirement is defined by the selected international or national standard.
What rebound resilience values are typical for common materials?
Typical indicative ranges are 40% to 65% for conventional flexible polyurethane foams, 55% to 75% for high-resilience grades, below about 20% for viscoelastic memory foams, and 50% to 90% for well-vulcanized rubber compounds depending on the polymer type and formulation. Actual values depend on the test method, temperature, and material grade, so comparison should always reference the same test conditions.
How does temperature affect rebound resilience results?
Rebound resilience is strongly temperature dependent. As temperature decreases toward the glass transition region of the polymer, the material becomes more viscous and the rebound rate drops significantly, while at elevated temperatures resilience generally increases. For this reason, tests at standard laboratory temperature must be strictly conditioned, and additional low-temperature or high-temperature testing is recommended for products used in demanding thermal environments.
Which standard should be selected for my product?
The choice depends on the material type and market requirements. Flexible polyurethane and polyolefin foams are normally tested to ISO 8307, ASTM D3574 Test H, or GB/T 6670, while vulcanized rubber and thermoplastic elastomers are tested to ISO 4662, GB/T 1681, or ASTM D2632. When a specific buyer specification or regulation applies, the referenced test method and its exact parameters should be confirmed before testing begins, and accredited third-party laboratories can advise on the most appropriate standard for the intended application.