ASTM D1056 is the key standard used to classify and specify flexible cellular rubber materials, often called sponge rubber or foam rubber. These materials are widely used for sealing, cushioning, vibration isolation, and insulation across industries such as automotive, aerospace, construction, and electronics.

This standard provides a classification system based on physical properties like density, compression-deflection, tensile strength, elongation, and resistance to various environmental factors. It ensures that cellular rubber products meet the necessary performance requirements for their intended applications.

This article explains the scope of ASTM D1056, the testing equipment, how the tests are performed, and related ASTM standards.

Purpose of ASTM D1056

ASTM D1056 provides a systematic way to classify flexible cellular rubber materials into types, classes, grades, and suffixes based on:

• Base Material (neoprene, EPDM, natural rubber, etc.)

• Physical Properties (compression resistance, tensile strength, density)

• Temperature Resistance

• Oil and Fuel Resistance

• Ozone and UV Resistance

• Flammability

Products that meet ASTM D1056 classifications give buyers confidence that the materials will perform consistently in demanding environments.

Equipment Required

Several standard pieces of equipment are needed to perform the tests outlined in ASTM D1056:

• Universal Testing Machine (UTM):

  • Used for tensile strength and elongation tests.

• Compression Fixtures:

  • Plates and spacers for measuring compression-deflection properties and compression set.

• Durometer Hardness Testers:

  • Special Shore OO, Shore A, or other appropriate durometer scales for soft materials.

• Environmental Chambers:

  • For heat aging, low temperature brittleness, and fluid immersion resistance testing.

• Oven and Humidity Chambers:

  • For accelerated aging tests at elevated temperatures and humidity.

• Special Cutting Tools:

  • Dies, punches, or other devices for preparing consistent specimen shapes and sizes.

Test Specimens

Specimens must be prepared according to the standard's dimensions for each type of test, typically:

• Rectangular or dumbbell-shaped specimens for tensile tests.

• Circular or rectangular specimens for compression-deflection tests.

• Specific thicknesses (commonly 6.3 mm or 0.25 in) for compression testing.

Care must be taken to avoid nicking, tearing, or otherwise damaging the specimens during preparation, as defects can lead to inaccurate results.

Test Procedures for ASTM D1056

Several tests are performed to classify a material under ASTM D1056:

1. Compression-Deflection Test:

   • The specimen is compressed to 25% of its original thickness at a specified rate.

   • The force required to achieve this compression is measured.

   • This value helps categorize the material’s firmness or softness.

2. Tensile Strength and Elongation:

   • Specimens are pulled in tension until failure.

   • Maximum force and elongation (percent stretch before breaking) are recorded.

   • Testing is typically performed following ASTM D412 procedures.

3. Compression Set Test:

   • A specimen is compressed to a set thickness and held under compression at elevated temperatures for a specified time.

   • After releasing, the specimen's permanent deformation is measured.

   • This test assesses a material’s ability to recover its shape after prolonged compression.

4. Density (Specific Gravity):

   • Specimens are weighed and measured to calculate density.

   • This determines material classification into low, medium, or high-density grades.

5. Water Absorption Test:

   • Specimens are immersed in water under controlled conditions.

   • The percentage increase in weight is measured to evaluate water absorption resistance.

6. Ozone Resistance Test:

   • Specimens are exposed to ozone-rich environments for a specified time and inspected for cracking or other deterioration.

7. Low Temperature Resistance:

   • Specimens are flexed or compressed at subzero temperatures to ensure they maintain flexibility and do not crack.

8. Fluid Immersion Tests:

   • Some materials are tested for changes in properties after immersion in oils, fuels, or other fluids, depending on their classification.

Each material is assigned a four-character grade that defines its compression properties, heat resistance, oil resistance, and special features (like ozone resistance).

Results and Reporting

A complete report for ASTM D1056 testing should include:

• Compression-deflection values.

• Tensile strength and elongation results.

• Compression set percentage.

• Density (or specific gravity).

• Hardness values (durometer reading).

• Results from environmental resistance tests (ozone, fluid immersion, low temperature).

• Detailed descriptions of specimen preparation and conditioning.

• Any deviations from the standard procedures.

Each of these results determines the material’s classification code under D1056, often requested directly in engineering drawings and specifications.

Related ASTM Standards

There are several important ASTM standards that are often used alongside or compared with ASTM D1056:

• ASTM D412 – Standard Test Methods for Vulcanized Rubber and Thermoplastic Elastomers—Tension:
  This method measures tensile strength and elongation of rubber materials and is directly used for part of the ASTM D1056 requirements.

• ASTM D395 – Standard Test Methods for Rubber Property—Compression Set:
  These methods are referenced for measuring the permanent deformation after compression, critical for sponge and foam rubber products.

• ASTM D2240 – Standard Test Method for Rubber Property—Durometer Hardness:
  Hardness measurements are taken according to D2240 using appropriate Shore scales based on the softness of the foam.

• ASTM D1171 – Standard Test Method for Rubber Deterioration—Surface Ozone Cracking Outdoors or Chamber (Triangular Specimens):
  This test evaluates a rubber’s resistance to ozone cracking, which is a crucial property for outdoor sealing and cushioning applications.

• ASTM D471 – Standard Test Method for Rubber Property—Effect of Liquids:
  Immersion testing in oils, fuels, and solvents is critical to verify that the cellular rubber resists swelling or degradation.

• ASTM D575 – Standard Test Methods for Rubber Properties in Compression:
  Although D575 is mainly for solid rubber, some compression data may be used for comparative purposes.

• ASTM D1055 – Standard Specification for Rubber Cellular Sheeting—Automobile Sponge:
  This standard specifically applies to automotive applications, especially for sponge rubber materials used in door seals and weatherstripping.

Applications of ASTM D1056 Testing

Materials tested and classified under ASTM D1056 are found in:

• Automotive Door Seals and Gaskets

• HVAC and Refrigeration Seals

• Electrical Enclosures (Gaskets and Weather Seals)

• Vibration Isolation Pads

• Medical Device Cushioning Components

• Construction Expansion Joints and Weatherproofing Systems

Products meeting ASTM D1056 classifications are relied upon to maintain tight seals, resist environmental degradation, and maintain flexibility over a wide range of temperatures and conditions.

Conclusion

ASTM D1056 offers a detailed and practical framework for specifying and qualifying flexible cellular rubber materials. By categorizing sponge and foam rubbers by compression, density, tensile properties, and environmental resistance, engineers and manufacturers can ensure consistent, high-performance material selection.
Testing to ASTM D1056, combined with related standards like ASTM D412 and ASTM D471, ensures that materials meet the rigorous demands of industrial and commercial applications.