Foam Material Rebound Resilience Testing: Principles, Standards, and Procedures

Rebound resilience testing measures the elastic recovery performance of foam materials by determining the height to which a steel ball rebounds after free fall onto a conditioned specimen. This article explains the testing principle, applicable standards such as ISO 8307, ASTM D3574, and GB/T 6670, specimen requirements, step-by-step procedures, and typical applications in the furniture, automotive, footwear, and packaging industries.

Technical Overview

Rebound resilience, also known as ball rebound resilience or rebound rate, is a fundamental mechanical property of flexible cellular polymeric materials. It quantifies the ability of a foam to store and return impact energy elastically. The test is performed by dropping a steel ball of specified mass from a fixed height onto a horizontally supported foam specimen and measuring the height the ball reaches after rebounding. The rebound resilience value is calculated as the ratio of the rebound height to the initial drop height, expressed as a percentage.

A high rebound value indicates a lively, elastic foam that quickly recovers its shape after deformation, which is desirable for seating, mattresses, and athletic applications. A low rebound value indicates a viscous, energy-absorbing foam, which is intentionally engineered in viscoelastic (memory) foam products and protective cushioning packaging. Because different foam families are designed for opposite performance goals, the rebound resilience test is an essential quality control and material selection tool rather than a simple pass-fail indicator of quality.

The most widely recognized test methods for this property are ISO 8307 (flexible cellular polymeric materials — determination of rebound resilience), ASTM D3574 Test H (ball drop rebound for slab, bonded, and molded urethane foams), and GB/T 6670 (determination of rebound resilience of soft foam polymeric materials). These methods share the same basic principle and differ mainly in apparatus details and reporting requirements.

Testing Samples

Flexible Polyurethane Foams

Conventional polyether and polyester slabstock polyurethane foams, molded automotive foams, and high-resilience (HR) grades are the most frequently tested materials. These foams are used in furniture cushions, mattresses, and vehicle seats, where rebound resilience directly influences sitting comfort, support, and long-term durability perception.

Viscoelastic and Latex Foams

Memory foam is tested to verify its intentionally low rebound behavior, which produces the characteristic slow-recovery feel. Natural and synthetic latex foams are tested to confirm their typically high elastic recovery, which supports their premium positioning in bedding products.

Thermoplastic and Polyolefin Foams

Cross-linked and non-cross-linked polyethylene foams, EVA foams used in footwear midsoles, and PVC or nitrile rubber foams used in sealing and cushioning are also evaluated. For these materials, rebound resilience correlates with energy return, cushioning efficiency, and vibration behavior.

Specimen Preparation Requirements

Standard practice requires block specimens with parallel, flat upper and lower surfaces, free of skins, cuts, densification lines, and other visible defects. A typical specimen size is approximately 100 mm x 100 mm in cross-section with a thickness of at least 50 mm, or the minimum dimension specified by the applicable product standard. Specimens must be conditioned in a controlled laboratory atmosphere, typically 23 ± 2 °C and 50 ± 5% relative humidity, for at least 16 to 24 hours before testing. Stacking thin sheets to reach the required thickness is generally not permitted because the interfaces alter the impact response.

Testing Items

The primary test item is the ball rebound resilience value, expressed as a percentage and reported as the average of multiple valid impacts performed at different positions on the specimen. Accredited third-party laboratories typically report the following information:

• Individual and mean rebound resilience values for each specimen and the overall mean for the sample lot
• Test standard applied (for example ISO 8307, ASTM D3574 Test H, or GB/T 6670)
• Ball mass, ball diameter, and drop height used
• Specimen dimensions, density where required, orientation, and the tested face
• Conditioning temperature, humidity, and laboratory test temperature
• Number of impacts and their positions relative to specimen edges

Rebound resilience testing is frequently combined with complementary foam characterization, including apparent density (ISO 845 or ASTM D3574 Test A), compression set (ASTM D3574 Test D), indentation force deflection (ASTM D3574 Test B1/B2 or EN ISO 2439), and fatigue testing, to build a complete mechanical performance profile of the material.

Testing Methods

Apparatus and Test Conditions

The test apparatus consists of a vertical guide tube or drop mechanism, a polished steel ball, a rigid horizontal base plate, and a height measurement system such as a graduated transparent scale, photoelectric sensors, or high-speed video capture. In ASTM D3574 Test H, for example, a steel ball of approximately 16 mm diameter and 16 g mass is dropped from a height of 500 mm onto the specimen. The measurement system must resolve rebound height accurately, and the ball must be kept clean and free of static charge, dust, and oil, since contamination or electrostatic adhesion can distort readings.

Test Procedure

• Condition the specimens to equilibrium in the standard laboratory atmosphere and verify the test room temperature before beginning.
• Measure and record specimen dimensions and, where required, calculate apparent density.
• Place the specimen on the rigid horizontal base with the intended service face upward, ensuring full support and no gaps.
• Position the drop mechanism vertically above the specimen, aligning the ball path with a point located well away from all edges and corners.
• Release the ball without initial velocity or spin and allow it to fall freely onto the specimen surface.
• Record the maximum rebound height reached by the ball using the scale or sensor system.
• Repeat the drop at several different positions on the specimen surface, spaced apart from one another and from the edges, discarding any visibly disturbed or permanently indented locations.
• Calculate rebound resilience for each valid impact and report the arithmetic mean value.

Calculation and Expression of Results

Rebound resilience is calculated as the rebound height divided by the drop height, multiplied by 100, and is reported as a percentage. Consistent drop height, accurate height resolution, uniform specimen support, and standardized conditioning are the key factors that ensure repeatability and reproducibility between laboratories.

Applications

Rebound resilience data are used across the entire foam value chain, from raw material development to finished product compliance:

• Furniture and bedding: differentiating conventional, high-resilience, latex, and memory foam grades for mattresses, toppers, and upholstered cushions
• Automotive: qualifying seat cushions, headrests, armrests, and interior trim foams against OEM material specifications
• Footwear: evaluating energy return and cushioning behavior of EVA and polyurethane midsole foams
• Packaging and protective equipment: confirming low-rebound, energy-absorbing behavior in cushioning foams for electronics and shock-sensitive goods, and high-rebound behavior in sports mats and padding
• Toys and consumer products: verifying elastic performance and consistency for safety-related and comfort-related foam components
• Manufacturing quality control: monitoring foaming process consistency, curing completeness, and batch-to-batch uniformity through statistical process control of rebound values

FAQ

What is a good rebound resilience value for foam?

There is no universal target value because the ideal rebound level depends on the application. As general industry reference ranges, conventional flexible polyurethane foams typically rebound around 40% to 55%, high-resilience grades often reach 55% to 75%, latex foams commonly fall between 50% and 70%, and viscoelastic memory foams are deliberately low, often below 20%. Product specifications, not the test itself, define the acceptable range.

Which standards govern rebound resilience testing of foams?

The principal methods are ISO 8307 for flexible cellular polymeric materials, ASTM D3574 Test H for urethane foams, and GB/T 6670 for soft foam polymeric materials. Many end-user specifications reference one of these methods directly, so the applicable standard should be confirmed before testing.

What specimen size is required?

A common requirement is a block of approximately 100 mm x 100 mm by at least 50 mm thickness with flat, parallel faces. Because thin specimens bottom out under the falling ball, very thin sheets may be unsuitable for this method, and stacking layers is usually not allowed. Specific dimensions should be verified against the governing standard or customer specification.

How is rebound resilience different from compression set or hardness?

Rebound resilience measures instantaneous elastic energy return under a dynamic impact. Hardness, measured by indentation force deflection or similar methods, characterizes resistance to quasi-static deformation. Compression set measures permanent height loss after prolonged static compression. The three properties are independent and together provide a complete picture of foam behavior.

What factors can affect the accuracy of the test?

Temperature and humidity conditioning, specimen flatness and support, surface skins or crushed cells, ball cleanliness and static charge, impact point spacing, and operator reading technique all influence results. Testing in an accredited third-party laboratory under controlled conditions minimizes these sources of variability.

Can finished products such as mattresses be tested directly?

The standard methods are designed for cut specimens, so testing is normally performed on material samples taken from the finished product. Testing a complete article does not conform to the standard because the cover materials, quilting layers, and overall thickness change the impact response.