ASTM D1056 is the standard specification for flexible cellular rubber products (sponge rubber and expanded rubber). It is the ASTM counterpart to ISO 6916-1, and the two are explicitly noted as similar specifications in ASTM D1056's own text.
Current Version and Scope
The current version is ASTM D1056-20, last updated in November 2020 and overseen by ASTM Committee D20 on rubber. It covers sponge rubber and expanded rubber, but excludes latex foam rubber and ebonite cellular rubber. The base material may be synthetic, natural, or reclaimed rubber, or a mixture, and may contain other polymers or additives.
Classification System
D1056 classifies cellular rubber by Types, Classes, Suffixes, and Grades:
Types: 1 and 2 (distinguishing open-cell vs. closed-cell structure)
Classes: A, B, C, and D (based on resistance properties such as oil resistance)
Grades: 0 through 5 (based on physical properties, notably compression-deflection)
The standard mandates specific test methods for the various grades, including accelerated aging, compression-deflection, oil immersion (open-cell), fluid immersion (closed-cell), water absorption, density, and low-temperature flex tests.
Relationship to Your Earlier Questions
This is the standard where the "2A5" designation you asked about earlier actually originates. In ASTM D1056, "2A5" corresponds to a closed-cell (Type 2), Class A (no special oil resistance requirement), Grade 5 cellular rubber. This is the classification system that commercial "2A5 EPDM" product data sheets typically reference.
The key distinction from ISO 6916-1 is unit convention: ASTM D1056 treats inch-pound units as the standard, with SI values provided only for reference. This affects how compression-deflection and other physical limits are expressed numerically.
Practical Note
If you are specifying EPDM sponge rubber, writing "ASTM D1056 2A5 EPDM" is a recognized industry shorthand. The "2A5" tells the supplier the required cell structure, resistance class, and firmness grade, while "EPDM" specifies the polymer. ASTM D1056 itself does not mandate EPDM for the 2A5 grade-just as with ISO 6916-1, the classification is material-agnostic, and the polymer must be called out separately.