What Is ASTM D1056?
ASTM D1056 is the Standard Specification for Flexible Cellular Materials — Sponge or Expanded Rubber. It classifies sponge and foam rubber materials used in sealing, cushioning, thermal insulation, vibration damping, and gasketing applications. The standard covers open-cell sponge rubber, closed-cell expanded rubber, and materials with a combination of open and closed cells.
D1056 designations encode the cell structure (open or closed), grade (compound type / service suitability), class (compression-deflection range), and optional suffix requirements for fluid resistance, low-temperature flexibility, and other special properties. It is one of the most referenced standards in industrial rubber purchasing, particularly for foam tapes, door seals, weather strip, and custom-cut sponge gaskets.
How to Read an ASTM D1056 Designation
| Element | Example | Meaning |
|---|---|---|
| Cell type prefix | 2 | 1 = open cell (sponge); 2 = closed cell (expanded rubber) |
| Grade letter | A | Compound / service suitability: A = general purpose, B = oil resistant, C = oil/fuel resistant (medium mass change), D = high-temperature resistant |
| Class number | 1 | Compression-deflection range (stiffness). Class 1 = softest; higher numbers = firmer. |
| Suffix letters | A, B, C… | Optional requirements: fluid immersion, ozone, low temperature, etc. |
For example, 2A1 identifies a closed-cell, general-purpose sponge rubber with the softest compression-deflection class — a very common designation for EPDM closed-cell weather strip and foam tape. The designation 1B3 identifies an open-cell, oil-resistant sponge with a medium-firm compression range.
Common ASTM D1056 Grades and Their Typical Materials
- Grade 1A — Open Cell / General Purpose: Synthetic, natural, or reclaimed rubber — no specific oil resistance required. Used in cushioning, packaging, and low-pressure seals.
- Grade 1B — Open Cell / Oil Resistant (Low Mass Change): Synthetic rubber meeting oil resistance with low mass change (−25 to +10% volume). Used in oil-exposed sealing and gasketing applications.
- Grade 2A — Closed Cell / General Purpose (Non-Fuel-Resistant): Synthetic, natural, or reclaimed rubber — no specific fuel resistance required. The most common grade for automotive door seals, window seals, and architectural weather strip.
- Grade 2B — Closed Cell / Fuel-Resistant (Low Mass Change): Synthetic rubber meeting fuel resistance with low mass change (≤50% for density >10 lb/ft³). Used where fuel or solvent splash resistance is needed with a tight swell limit.
- Grade 2C — Closed Cell / Fuel-Resistant (Medium Mass Change): Closed-cell synthetic rubber with medium fuel swell tolerance (≤150% mass change for density >10 lb/ft³; ≤250% for density ≤10 lb/ft³). Any qualifying synthetic rubber compound. Used where fuel or solvent splash resistance is required and medium mass change is acceptable.
- Grade 2D — Closed Cell / High-Temperature Resistant: Closed-cell rubber rated for extreme temperature service from −103 to 347 °F (−75 to 175 °C). Any qualifying synthetic rubber compound meeting the basic requirements. Mandatory low-temperature flex at −67 °F and compression set at 212 °F are basic requirements. No specific oil resistance required.
Frequently Asked Questions — ASTM D1056
What is the difference between open cell and closed cell sponge rubber in D1056?
Open-cell (Type 1) sponge rubber has interconnected cells that allow air and fluid to pass through the material. It is softer and more compressible but absorbs liquids. Closed-cell (Type 2) expanded rubber has sealed, independent cells that resist fluid ingress and provide a barrier seal. Closed-cell materials are preferred for weather sealing, water exclusion, and thermal insulation; open-cell is preferred for cushioning, acoustic absorption, and ventilation applications.
What does the Class number mean in an ASTM D1056 designation?
The Class number in D1056 specifies the compression-deflection range — essentially, how firm or soft the material is under load. Class 1 is the softest, requiring the least force to compress a specified percentage. Higher class numbers indicate progressively firmer materials. Selecting the correct class ensures the seal or cushion compresses appropriately under the clamping force or application load.
What rubber compounds are typically used for ASTM D1056 Grade 2A closed-cell sponge?
Grade 2A (closed cell, general purpose / non-fuel-resistant) permits synthetic, natural, or reclaimed rubber — the standard does not specify a required polymer. The compound must meet the basic physical requirements of Table 2: heat aging (±30% compression deflection change after 168 h at 158°F) and water absorption limits. The compounder selects the elastomer to meet those requirements for the target application.
How does ASTM D1056 relate to MIL-C-3133 and ASTM D6576?
ASTM D1056 is a broad specification for sponge and expanded rubber covering multiple manufacturing methods. MIL-C-3133 is an older US military specification for sponge rubber that preceded D1056 and is now largely superseded by it. ASTM D6576 is a separate, more recent standard that specifically covers chemically blown cellular rubber. D1056 designations and D6576 designations are not directly interchangeable even for similar materials.
Can ASTM D1056 sponge rubber be used for outdoor weathering applications?
Yes, with the right grade selection. Grade 2A (closed cell, non-fuel-resistant) is widely used in automotive and construction weather sealing. Grade A and B open-cell materials require weathering evaluation specific to the compound selected — the standard does not restrict or name the polymer, so outdoor durability depends on the actual elastomer the compounder uses. Always verify the specific compound’s ozone and UV resistance for outdoor applications.