Comparing Rubber Compounds: Material Properties

Material properties for rubber compounds include physical, thermal, and electrical properties. Elasto Proxy specializes in industrial rubber products and helps its customers with compound selection.

This article compares four of the compounds that we commonly distribute or fabricate.

• EPDM
• Nitrile (NBR, Buna-N)
• Neoprene
• Silicone

It also compares three additional compounds that are used less commonly but are still important. 

• Natural rubber
• SBR
• Fluorosilicone

Keep reading to learn how rubber compounds compare. If you’re ready to discuss your sealing application, contact us.

Physical Properties: Material Properties for Rubber Compounds

The physical properties of rubber compounds are material characteristics that don’t involve a change in chemical composition.

Tensile Strength

Tensile strength describes the amount of force needed to pull a rubber sample apart until it breaks. It’s measured in either pounds per square inch (psi) or kilopascals (kPa).

EPDM and neoprene have the same tensile strength – and in an amount that’s twice as great as silicone.

Natural rubber has the greatest tensile strength. Fluorosilcione’s is the worst.   

Hardness

Hardness describes a rubber’s resistance to indentation. It can be measured on the international rubber hardness degree (IRHD) scale from 0 (softest) to 100 (hardest).

EPDM, neoprene, and nitrile are all available in the same range of hardnesses. Silicone is available in softer IRHDs, but not in ones that are as hard as these other compounds.      

Natural rubber comes in IHRDs that are as soft as silicone. SBR is similar to neoprene and nitrile in terms of available hardnesses. Fluorosilcone has a relatively narrow range of IRHDs.  

Specific Gravity

Specific gravity is the ratio of the weight of a material to the weight of an equal volume of water at a specified temperature. It’s a dimensionless number, but rubber with a higher specific gravity is heavier.

Compared to neoprene and nitrile, silicone is heavier and EPDM is lighter.  

Fluorosilicone has the highest specific gravity. Natural rubber and SBR have similar levels.

Tear Resistance

Tear resistance describes a rubber’s resistance to the growth of a nick or cut under tension. It includes the force required to initiate a tear and the force required to propagate it.

Neoprene has the greater tear resistance. Silicone has the least. Nitrile’s is only fair.   

Natural rubber has much greater tear resistance than the other compounds.

Abrasion Resistance

Abrasion resistance describes a rubber’s resistance to rubbing or scraping.

Silicone has the weakest abrasion resistance, but nitrile’s is excellent. EPDM and neoprene are both good.

Natural rubber has excellent abrasion resistance, but SBR’s is very good.

Rebound (Cold and Hot)

Rebound refers to a rubber’s ability to regain its original size and shape after it’s temporarily deformed. This physical property is affected by temperature, which is why Cold and Hot values are listed below.

These four compounds are comparable in terms of both Cold and Hot rebound.

These three compounds have comparable rebound levels.

Compression Set

Compression set refers to the permanent deformation that occurs when a material is compressed under a specific load for a specific time and at a specific temperature.

Silicone and neoprene are more susceptible to compression set than EPDM and nitrile.

Like silicone, fluorosilicone has only fair compression set. Natural rubber and SBR are both good.

Gas Permeability

Gas permeability describes the rate at which gas molecules such as air pass through a rubber compound.

Neoprene has good gas permeability. EPDM, nitrile, and silicone do not.

Natural rubber, SBR, and fluorosilicone are comparable.

Water Absorption

Water absorption refers to a rubber’s ability to absorb water from its environment. Compounds where the water absorption is described as Very Good or Excellent absorb very little water.

Silicone has the lowest water absorption, but EPDM’s can also be excellent. Neoprene and nitrile are b oth good.

These three compounds have low rates of water absorption.

Oxidation

Oxidation adds oxygen to a substance. With rubber, that’s a problem because a compound can become weaker and less elastic.

EPDM and silicone have greater resistance to oxidation than either nitrile or neoprene. 

Fluorosilicone has excellent oxidation resistance, but SBR’s is only fair.

Ozone

Ozone is an atmospheric gas that breaks a compound’s molecular bonds and can cause a form of cracking called dry rot.

EPDM and silicone both have excellent ozone resistance. Nitrile’s is only fair.

Fluorosilicone is excellent. Natural rubber and SBR both have poor ozone resistance.

Sunlight Aging

The sun’s ultraviolet (UV) rays destroy a compound’s molecular bonds and cause a loss of strength, elasticity, and flexibility. Sunlight aging describes how well a rubber resists UV damage.

EPDM and silicones are the best choices, but neoprene is also very good. Nitrile is poor.

Fluorosilicone is a very good choice for sunlight aging. Natural rubber and SBR are both poor choices.  

Thermal Properties: Material Properties for Rubber Compounds

Thermal properties indicate how well a compound performs under or withstands heat and cold.

Service Temperature

Service temperatures are the highest and lowest temperatures at which a compound can be used.

Silicone withstands the coldest and hottest temperatures as well as the widest range of temperatures.

Natural rubber withstands the coldest temperatures. Flurosilicone withstands the hottest.

Heat Aging (Continuous Service Limits)

Heat aging, a reduction in material properties, occurs naturally as a compound is exposed to normal service temperatures over time.

Silicone resists heat aging across the widest range of temperatures, including the most extreme temperatures.

Fluorosilicone has the best heat aging performance.

Electrical Properties: Material Properties for Rubber Compounds

Electrical properties refer to a material’s ability to conduct or resist the flow of electricity.   

Dielectric Strength

Dielectric strength describes a compound’s resistance to dielectric breakdown, the point at which an insulating material stops preventing current from flowing under electrical stress.

EPDM has the best dielectric strength. Nitrile has the worst. Neoprene and silicone are both good.

Natural rubber and SBR both have excellent dielectric strength.  Fluorosilicone’s is good.

Electrical Insulation

Electrical insulation describes a compound’s resistance to the flow of electrical current. It’s different than dielectric strength, which is a function of voltage.   

EPDM and silicone both have excellent electrical insulation. Nitrile is a poor electrical insulator, however.

Fluorosilcione is the best electrical insulator, but all three compounds provide strong performance.

Ask Elasto Proxy for Help Comparing  Compounds

Are you an engineer? Do you need help comparing compounds for industrial sealing? For more information about compound selection, contact Elasto Proxy.