Rebound rate testing, also known as rebound resilience testing, quantifies the elastic recovery performance of flexible foams, rubbers, and elastomers by measuring the percentage of impact energy returned after a controlled collision. This article provides a complete technical reference to rebound rate test methods based on ISO, ASTM, and GB standards, covering sample requirements, test procedures, calculation formulas, result evaluation, and typical industry applications for engineers and quality control professionals.
Technical Overview
Rebound rate (rebound resilience) is a fundamental mechanical property that describes how much impact energy a cushioning material returns after being deformed by a striking body. It is expressed as the ratio of the rebound height (or rebound energy) to the initial drop height (or impact energy), multiplied by 100%. The rebound rate is a key indicator for classifying flexible polyurethane foam grades, evaluating viscoelastic (memory) foam behavior, and assessing the dynamic elasticity of vulcanized rubber products.
The rebound rate is calculated using the following general formula:
- R = (H2 / H1) x 100%, where H1 is the initial drop height or impact energy and H2 is the maximum rebound height or returned energy.
- A higher rebound rate indicates a more elastic, energy-returning material, such as high-resilience (HR) foam.
- A lower rebound rate indicates a more energy-absorbing material, such as slow-rebound memory foam used in comfort and pressure-relief applications.
Rebound rate testing is typically performed by accredited third-party laboratories or in-house quality control departments using standardized equipment, most commonly a ball rebound tester or a pendulum rebound apparatus, in accordance with ISO 8307, ASTM D3574 (Test H), GB/T 6670, ISO 4662, and GB/T 1681.
Testing Samples
Conventional and High-Resilience Flexible Polyurethane Foam
Standard slabstock and molded polyurethane foams used in mattresses, seat cushions, and furniture padding are the most frequently tested materials. High-resilience foam is generally expected to achieve a rebound rate of 55% or higher, while conventional polyether foams typically fall in the range of 35% to 50%.
Viscoelastic (Memory) Foam
Slow-rebound memory foam is deliberately formulated for low resilience, with rebound rates typically below 10% to 15%. Testing verifies the slow-recovery behavior required for pressure-relief mattresses, pillows, and medical cushioning products.
Vulcanized Rubber and Thermoplastic Elastomers
Rubber sheets, seals, dampers, shoe outsoles, and TPE components are evaluated using pendulum-type rebound resilience methods, which measure the energy returned by the elastomer under a defined impact velocity.
Other Cellular and Cushioning Materials
Latex foam, EVA and PE foams, packaging inserts, sports protective padding, helmet liners, and acoustic cushioning materials can also be characterized for rebound performance using adapted versions of the standard methods.
Testing Items
A rebound rate test program typically includes the following measured and reported parameters:
- Ball rebound resilience (%) at a 500 mm drop height with a 16 g steel ball.
- Pendulum rebound resilience (%) for rubber and dense elastomers.
- Maximum rebound height (mm) recorded after each impact.
- Rebound rate classification: high resilience, conventional, or slow rebound.
- Comparison against product specifications or purchasing agreement limits.
- Optional related properties: density (kg/m3), indentation force deflection (IFD/ILD), compression set, and hardness, which help interpret rebound behavior.
Testing Methods
Sample Preparation and Conditioning
Specimens are usually cut to 100 mm x 100 mm x 50 mm with parallel top and bottom surfaces, free of skin defects, cracks, and visible cell damage. Unless otherwise specified, samples must be conditioned at 23 +/- 2 degrees C and 50 +/- 5% relative humidity for at least 16 hours before testing. Specimens should not be compressed or stressed during transport or storage, and testing should be completed within the time window defined by the applicable standard.
Ball Rebound Method (ISO 8307, ASTM D3574 Test H, GB/T 6670)
The ball rebound method is the primary approach for flexible cellular materials. A polished steel ball with a mass of approximately 16 g is dropped in free fall from a height of 500 mm onto the horizontal specimen surface. The maximum rebound height is captured using optical sensors, photodiode arrays, or high-speed video measurement.
The general test procedure is as follows:
- Place the conditioned specimen on a rigid, level base plate without additional clamping.
- Align the ball release mechanism so the ball strikes the center of the test area perpendicular to the surface.
- Perform preliminary conditioning drops as required by the standard, then record the rebound heights of the valid drops.
- Test at least three different positions on the specimen surface, keeping impact points at least 20 mm apart and away from edges.
- Calculate the rebound rate as the average of the valid results and report it to the nearest 1%.
Pendulum Rebound Method (ISO 4662, GB/T 1681)
For vulcanized rubber and dense elastomers, a pendulum with a defined striker mass and impact energy swings against a clamped specimen. The rebound resilience equals the ratio of the rebound swing height to the initial drop height of the pendulum arm, expressed as a percentage. This method evaluates dynamic elasticity under impact conditions closer to real service loading for rubber components.
Calculation and Result Evaluation
Results are interpreted against common industry reference ranges:
- High-resilience (HR) foam: rebound rate of 55% and above.
- Conventional flexible polyurethane foam: approximately 35% to 50%.
- Slow-rebound (viscoelastic) foam: typically below 10% to 15%.
Major factors that influence test results include foam density and cell structure, specimen thickness, temperature and humidity, impact position, ball surface condition, and specimen aging history. Repeat testing and strict environmental control are essential for reproducible results.
Applications
Rebound rate testing supports material selection, product certification, and quality control across many industries:
- Mattress and bedding: distinguishing high-resilience comfort layers from slow-rebound memory foam layers.
- Furniture and upholstered seating: verifying cushion elasticity, durability expectations, and supplier specifications.
- Automotive interiors: evaluating seat cushions, headrests, and armrests for comfort and energy absorption.
- Footwear: characterizing midsole elasticity and energy return for athletic and comfort shoes.
- Sports and protective equipment: optimizing helmet liners, padding, and shock-absorbing components.
- Packaging and logistics: selecting cushioning foams with appropriate energy absorption for fragile goods.
- Medical and pressure-care products: confirming the low-rebound behavior required for pressure-ulcer prevention cushions.
FAQ
What is a good rebound rate for polyurethane foam?
For high-resilience grade foam, a rebound rate of 55% or higher is generally expected. Conventional foam typically measures 35% to 50%, while genuine slow-rebound memory foam usually registers below 10% to 15%. Acceptance limits should always be defined in the product specification or purchase agreement.
Which standard should I choose for my material?
Flexible cellular materials such as polyurethane foam are best tested with ISO 8307, ASTM D3574 Test H, or GB/T 6670 using the ball rebound method. Vulcanized rubber and dense elastomers are better suited to the pendulum method described in ISO 4662 or GB/T 1681.
Can memory foam be tested with the same ball rebound method?
Yes. Memory foam is tested with the same ball rebound apparatus, and the low measured rebound value is precisely what confirms its slow-recovery, energy-absorbing character rather than indicating a defect.
How is rebound rate different from hardness or density?
Rebound rate measures dynamic energy return, while hardness (such as IFD/ILD) measures static resistance to indentation, and density measures mass per unit volume. The three properties are complementary, and reputable material specifications evaluate them together.
How should testing be arranged for compliance purposes?
For regulatory, contractual, or certification needs, testing should be conducted by accredited third-party laboratories that can issue standards-based test reports traceable to recognized calibration, clearly stating the applied standard, specimen details, conditioning environment, and individual and average results.