Determination of Volume Reduction Rate of Materials: Principles, Standards, and Test Methods

Determination of volume reduction rate is an essential physical performance test that quantifies the percentage decrease in a material's volume after exposure to compressive stress, elevated temperature, or long-term aging. Governed by internationally recognized standards such as ISO 1856, ASTM D395, and ASTM D3574, this test is widely used to evaluate the dimensional stability and long-term reliability of foams, rubbers, and insulation products. This article explains the measurement principles, sample requirements, test procedures, calculation methods, and typical industrial applications.

Technical Overview

Volume reduction rate determination is a laboratory test that measures how much a material permanently loses in volume after being subjected to compression, heat, humidity, or cyclic environmental aging. The result is expressed as a percentage comparing the final recovered volume against the original volume of the specimen. A low volume reduction rate indicates that the material retains its shape, thickness, and functional performance over time, while a high value signals permanent deformation, loss of resilience, and potential premature failure in service.

Definition and Calculation

The volume reduction rate is calculated using the following relationship: Volume Reduction Rate (%) = (V0 − V1) / V0 × 100, where V0 is the original specimen volume before the test and V1 is the specimen volume after compression, conditioning, and the specified recovery period. For specimens with uniform cross-sections, volume may be derived from dimensional measurements of length, width, and thickness; for irregular shapes, volume is typically determined by geometric survey or calibrated displacement methods.

Why the Test Matters

• It predicts the long-term sealing capability of gaskets, O-rings, and cushioning components.
• It verifies that thermal insulation products maintain their installed thickness and thermal performance.
• It supports quality control during raw material selection, formulation development, and incoming material inspection.
• It provides evidence for compliance with international material specifications and customer technical requirements.

The most commonly referenced standards include ISO 1856 (flexible cellular polymeric materials — determination of compression set), ISO 7214 (cellular plastics made from polyethylene), ASTM D395 (rubber compression set), ASTM D3574 (flexible urethane foams), ASTM D3575 (flexible cellular olefin materials), GB/T 8811 (dimensional stability of rigid cellular plastics), and relevant parts of the IEC 60811 series for cable insulation and sheathing materials.

Testing Samples

Flexible Cellular Foams

Polyurethane foams, polyethylene foams, and other flexible cellular materials are among the most frequently tested sample types. Specimens are usually prepared as rectangular blocks with standard dimensions, cut from sheet stock with clean, parallel faces and no visible skin defects or cell damage.

Rubber and Elastomeric Seals

Compression-molded or die-cut rubber specimens, including cylindrical buttons and rectangular pads of materials such as EPDM, silicone, nitrile rubber, and neoprene, are tested to evaluate sealing integrity under sustained compression.

Thermal Insulation Products

Preformed pipe insulation, rigid foam boards, elastomeric insulation sheets, and mineral wool products are tested to confirm that installed thickness and thermal resistance are preserved after service-like compressive and thermal exposure.

Cable Insulation and Sheathing Compounds

Polymeric compounds used in wire and cable construction are evaluated for shrinkage and volume stability after oven conditioning, ensuring reliable electrical and mechanical performance over the cable lifetime.

Rigid Cellular Plastics

Rigid polyurethane, polystyrene, and phenolic foams used in structural and insulation applications are assessed for dimensional and volumetric stability after exposure to defined temperature and humidity conditions.

Testing Items

Typical test items assessed under volume reduction rate determination include:

• Compression set under constant deflection at ambient, elevated, or low temperatures.
• Compression set under constant load (constant stress) conditions.
• Volume reduction rate after thermal aging in a forced-air oven.
• Dimensional and volumetric stability after temperature and humidity cycling.
• Shrinkage of cable insulation and sheath materials after oven treatment.
• Recovery ratio and residual deformation after a defined recovery period.
• Comparative volume loss between raw material batches or competing formulations.

Testing Methods

Constant-Deflection Compression Method

In this widely used approach, the specimen is compressed to a fixed percentage of its original thickness, typically 50%, 75%, or another value specified by the product standard. The compressed specimen is held in a fixture and exposed to a defined temperature for a set duration, commonly 22 to 24 hours or longer depending on the specification. After release, the specimen is allowed to recover for a standard period, often 30 minutes to 24 hours, before final dimensions are measured and the volume reduction rate is calculated. This method follows the principles of ASTM D395 Method B and ISO 1856 Method A.

Constant-Load Compression Method

Here, a constant force is applied to the specimen instead of a fixed deflection, simulating service conditions where a component supports a defined load. The specimen is conditioned under load at the specified temperature, then unloaded and measured after recovery. This approach corresponds to ASTM D395 Method A and is particularly relevant for seals and bearing pads evaluated under realistic stress levels.

Thermal Aging Combined Method

Specimens may be subjected to accelerated thermal aging in a ventilated oven at elevated temperatures, sometimes combined with compression or humidity exposure, before volume measurement. This method accelerates the physical and chemical changes that drive permanent volume loss, allowing laboratories to estimate long-term material behavior within a practical test window.

Measurement Techniques

Specimen dimensions are measured using calibrated instruments appropriate to the material stiffness. Rigid specimens are measured with precision callipers or micrometers, while soft cellular materials require low-pressure thickness gauges or optical and laser-based non-contact systems to avoid artificial deformation during measurement. All measurements are performed in a conditioned laboratory environment, typically 23 °C ± 2 °C and 50% ± 5% relative humidity, unless the governing standard specifies otherwise.

The final result is reported as the volume reduction rate percentage, together with test temperature, compression ratio, exposure duration, recovery time, and specimen dimensions, so that results are fully traceable and comparable between laboratories.

Applications

Volume reduction rate determination supports product development and quality assurance across a broad range of industries:

• Building and construction: verifying that pipe insulation and foam boards retain thermal performance after installation and years of service.
• Automotive: evaluating door seals, gaskets, seat cushioning, and vibration-damping foams for long-term compression resistance.
• Wire and cable: confirming that insulation and sheathing compounds resist shrinkage and volume loss under thermal stress.
• Packaging and logistics: assessing cushioning foams that must protect goods under sustained stacking loads.
• HVAC and refrigeration: ensuring elastomeric insulation maintains sealed, condensation-resistant coverage around chilled lines.
• Aerospace and rail transit: qualifying lightweight foam and rubber components that experience combined thermal, vibration, and compressive loading.
• Material research: comparing formulations, flame retardant loadings, blowing agent systems, and curing conditions during product development.

Manufacturers frequently engage accredited third-party laboratories to perform these tests, ensuring impartial results that satisfy regulatory requirements, customer specifications, and certification programs.

FAQ

What is the difference between volume reduction rate and compression set?

Compression set traditionally describes the residual decrease in thickness of a specimen after compression, while volume reduction rate expresses the equivalent loss as a volumetric percentage. For specimens with uniform geometry, the two results are closely related, and both quantify the same underlying phenomenon of permanent deformation.

What sample sizes are typically required?

Requirements depend on the governing standard and material type. Common flexible foam specimens are rectangular blocks, for example 50 mm × 50 mm × 25 mm, while rubber compression set buttons are typically cylindrical specimens of approximately 13 mm thickness. Laboratories should be consulted for exact dimensions and the minimum number of specimens, usually at least three per condition.

How long does a typical test take?

A standard 22-hour or 24-hour compression exposure at elevated temperature, followed by a 30-minute to 24-hour recovery period, can be completed within one to three working days including conditioning. Extended aging programs of 70 hours, 168 hours, or longer are available when required by the product specification.

What do a high or low result indicate?

A low volume reduction rate indicates strong elastic recovery and dimensional stability, meaning the material will likely maintain its sealing, cushioning, or insulating function over time. A high value indicates permanent deformation and suggests the material may loosen, leak, lose thermal efficiency, or fail mechanically in service.

Which factors can influence the test result?

Key influencing factors include test temperature, compression ratio, exposure duration, recovery time, specimen preparation quality, cell structure of foamed materials, measurement pressure applied during dimensioning, and environmental conditioning of the specimen before testing. Strict adherence to the specified standard method is essential for reproducible, comparable results.