Rubber Classifications

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

This page 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 the seal will be exposed to


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)


Classification of Flexible Cellular Materials

All of Cooper Standard ISG’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
  • Z. 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)