Rubber Bellows Materials Guide: EPDM, Silicone & Neoprene Bellows Comparison

The industrial bellows must withstand movement, pressure and harsh conditions. Three elastomers make up nearly all bellows manufactured today. The choice will impact both service life and total part cost.

The rubber bellows materials are the most important part of any design. Any minor compound changes create large differences in performance. The rubber bellows materials require careful evaluation before final selection. EPDM, silicone and neoprene are the three most common options.

EPDM Bellows

This material is based on an ethylene propylene diene rubber (EPDM) base. It is available across a shore hardness range of 40 to 90A. It provides unmatched steam resistance across all common elastomer options.

The FDA approved grades are available for food and beverage applications. It provides consistent and reliable electrical insulation across most voltages. It exhibits very low gas permeability for sealed system applications. It offers strong resistance to all common polar fluids. It performs very poorly when exposed to petroleum based oils.

One of the most underrated benefits of EPDM bellows is consistent flex life. It retains its mechanical properties through millions of full compression cycles. It does not become brittle after extended exposure to outdoor weather. It will degrade rapidly on contact with gasoline or diesel fuel.

Most manufacturers hold a large stock of standard sizes of this material. It remains the lowest cost option for most water based applications.

Silicone Bellows

This material is built from a polydimethylsiloxane polymer structure. It is offered across a shore hardness range of 20 to 80A. Fully biocompatible medical grades are available for implantable applications.

The transparent varieties can be supplied for visual inspection requirements. It exhibits extremely low compression across all temperature ranges. It offers the highest thermal stability of any common elastomer bellow. It has naturally non stick surface properties for low friction applications.

The silicone bellows are the best option for extreme temperature applications. They will retain flexibility even after thousands of hours at maximum temperature. They do not transfer taste or odour to any materials they contact. They are not recommended for applications with high dynamic tear loads.

Many manufacturers offer custom moulded versions at relatively low volumes. They remain the most expensive option of the three common materials. They show almost no change in hardness across their full operating range.

Neoprene Bellows

This material uses a chloroprene rubber composition as its base. It is available across the widest shore hardness range of 30 to 95A. It offers good inherent flame resistance for industrial applications. It provides moderate oil resistance for general purpose industrial use.

It has natural self extinguishing characteristics when exposed to open flame. It exhibits very good adhesion to most common structural metals. It has fair low temperature flexibility for most indoor applications. Its primary weakness is susceptibility to ozone cracking.

The neoprene bellows provide a balanced set of properties with no major extreme weakness. They remain the most common choice for general purpose industrial use. They will crack and fail prematurely if used outdoors unprotected.

Most manufacturers will recommend this material for unknown general applications. They offer the best value for applications with no extreme requirements.

Comparing Materials Properties

1. Operating Temperature Limits

Silicone offers a continuous use range from -65°F up to 450°F. EPDM offers a reliable working range from -65°F up to 300°F. Neoprene has a maximum continuous service temperature of 250°F. Neoprene also has the highest minimum operating temperature of -40°F.

Silicone handles sustained extreme heat better than any other option. EPDM remains the only suitable option for continuous steam exposure. Neoprene will degrade rapidly at temperatures above 220°F in the long term.

The selection for the rubber bellows materials for temperature should always consider long term continuous use. The short term peak temperatures can be 20% higher than the stated limits. This is the single most common cause of premature bellow failure.

Most application failures can be traced back to incorrect temperature selection. The manufacturers select the rubber bellows materials for this property.

2. Chemical Compatibility

EPDM offers excellent resistance to acids, bases, ketones and alcohols. Silicone offers moderate resistance to most oils, greases and weak acids. Neoprene offers the best resistance to refrigerants and mild acids. 

EPDM is the strongest available option for all polar chemical applications. Silicone has only moderate general chemical resistance across most categories. Neoprene is the best option for exposure to halogenated compounds.

Their compatibility should always be confirmed for continuous exposure conditions. The short term contact will often allow use outside of the stated ratings. 

Many compatibility charts will overstate resistance for intermittent contact. It is always recommended to test a sample before a full production run. EPDM bellows remain the default choice for water and chemical treatment applications.

3. Mechanical Performance

The silicone has a tensile strength rating between 1000 and 1500 PSI. EPDM has a tensile strength rating between 1500 and 2500 PSI. Neoprene has the highest tensile strength between 2000 and 3500 PSI.

Neoprene also exhibits the highest tear resistance of the three materials. EPDM offers the highest elongation properties for large movement applications. Silicone exhibits by far the lowest compression set of any common material.

Dynamic applications will place very different demands than static applications. High cycle applications will prioritise elongation and flex fatigue resistance. Static sealing applications will prioritise compression set above all other properties.

Most designers will select the wrong material for high cycle applications. Small differences in mechanical properties lead to very large differences in lifespan. The silicone bellows have a consistent seal for decades.

4. Service Life and Durability

Silicone will withstand over 20 years of continuous outdoor exposure. EPDM will provide between 15 and 20 years of reliable outdoor service. Neoprene will provide between 10 and 15 years of typical outdoor lifespan.

UV degradation rates vary significantly between different material grades. Ozone resistance is the single largest factor affecting long term outdoor lifespan. Flex fatigue resistance varies substantially between different base compounds.

Most manufacturers will quote a lifespan for ideal laboratory conditions. The proper design of the bellow geometry will have as much impact as the material. Their selection for lifespan will almost always provide the best long term value. The neoprene bellows are used in indoor protected applications.

Conclusion

The optimal material selection starts with clear application requirements. The silicone delivers unmatched performance at extreme high and low temperatures. It remains the best option for static sealing and biocompatible use. 

EPDM offers the best resistance to steam, acids and long term weather. It is the lowest cost option for most outdoor and chemical applications. Neoprene occupies a balanced middle ground between the other two. It offers good mechanical strength and flame resistance at a low cost.  Most manufacturers can provide test samples for validation before production.

Different rubber materials are best for different temperatures, chemicals and working environments. We break down the differences between EPDM, silicone and neoprene bellows to help you pick the right one for your job. To get personalized advice on the best material for your use case, reach out to us at +1 917-730-4350 or email info@customrubberbellows.com at any time