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Rubber Classifications

Open Cell vs. Closed Cell, Sponge vs. Dense. Rubber is classified by many physical properties but generally falls under two primary classifications: Dense and Sponge rubber.

This section outlines properties that are necessary to consider when designing a seal or gasket product.


Choosing the right sponge product is important in proper seal and gasket design. Engineers must consider the following:

      • Force in pounds per square inch required for proper closing
      • How the seal responds to compression over time or to being compressed and released
      • The elements to which the seal will be exposed

The below technical information will serve as a guide to comparing materials with their physical properties. We also give a brief synopsis on how we classify flexible cellular materials based on:

      • Type: Open or closed cell
      • Class: A, B, C, or D (characteristics of a material)
      • Grade: 0 through 5 (compression deflection rating)
      • Line call outs: (special industry specifications met)
      • Suffix: A, B, C etc. (special tests required)

* The range of properties that can be developed for any given polymer is limited by the material itself, and will vary within that range with compound formulation. All properties in a particular class are not found in a single compound. This information in this chart is general in nature. Consult with Lauren’s engineering team about the right compound for your application. 

Classification of flexible cellular materials

All of Lauren Manufacturing’s sponge products are identified by a three-character Grade Number (example: 2A2) per ASTM D-1056. The three characters represent type, class and grade, and are defined as follows:


      • Type 1 = Open cell
      • Type 2 = Closed cell


Once testing is complete, a Line Call Out is assigned to the compound according to the basic and Suffix Requirements the compound met.

Suffix Letter Test Required

      • A. Heat resistance
      • B. Compression set
      • C. Ozone or weather resistance
      • D. Compression deflection resistance
      • E. Fluid resistance (Fuel B)
      • F. Low temperature resistance
      • G. Tear resistance
      • H. Abrasion resistance
      • I. Adhesion resistance
      • J. Water absorption
      • K. Flammability resistance
      • L. Impact resistance
      • M. Staining resistance
      • N. Resilience
      • O. Density
      • P. Any special requirements


      • Class A = Non-oil resistant (example: EPDM)
      • Class B = Oil resistant, low swell (example: Nitrile)
      • Class C = Oil resistant, medium swell (example: Neoprene)
      • Class D = Extreme temperature resistance (example: Silicone)


Grade ratings represent compression deflection, or the amount of force in pounds per square inch to deflect the sample 25% of its height. They are as follows:

      • Grade 0 = less than 2 psi
      • Grade 1 = 2-5 psi
      • Grade 2 = 5-9 psi
      • Grade 3 = 9-13 psi
      • Grade 4 = 13-17 psi
      • Grade 5 = 17-25 psi

Example Line Call Out for Sponge

ASTM D-1056 2C2 A1 B2 E1 Z
(Z = material passes FMVSS 302)

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