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Exhaust Bellows

The Flexible Exhaust Products business unit of TRU-FLEX is engaged in the research, development, design and application of a range of technologies centered around exhaust bellows which are sometimes referred to as corrugated flexible pipe or some other similar terms.

Most commonly, exhaust bellows are designed to limit the motion/kinetic energy within or passed along from the engine to high-cost emissions systems by absorbing displacements and vibrations and accommodating thermal expansion. All TRU-FLEX flexible metal exhaust products can help customers remain compliant with international internal combustion engine emissions standards such as EPA Tier 4, Euro 4, 5 & 6, China 5 & 6, India BS 5 & 6, and so on.


TRU-FLEX exhaust bellows can be found On Engine, Between Turbos, Between Turbo and Aftertreatment and even between Aftertreatment and the Silencer or Outlet Pipe for On- and off-highway commercial vehicle exhaust systems for:

  • Trucks
  • Construction
  • Marine
  • Buses
  • Forestry
  • Power Generation
  • Tractors
  • Mining
  • Military


Standard Bellows

The first and most common combination of features is what we like to call “Standard Bellows.” TRU-FLEX's standard bellows offer excellent thermal expansion and vibration/motion control while meeting industry required leak specifications. They also deliver extremely long fatigue life if no torsional motion is present.


  • Corrugated stainless steel body
  • Internal polylock liner (optional)
  • External braid (optional)
  • External mesh (optional)
  • Vibration damping mesh (optional)

Severe Duty Bellows

TRU-FLEX’s Severe Duty Bellows is the second sub-grouping of products and they are aimed at offering excellent durability in difficult applications. In addition this design combination reduces static loss and has superior thermal insulating properties when compared to standard bellows. The robust design withstands severe displacements and includes a braided exterior that protects the bellows from external damage.


  • Corrugated stainless steel body
  • Internal polylock liner
  • External braid
  • Vibration damping mesh (optional)

Torsional Bellows

The third family to discuss is the Torsional Bellows. It is basically the Standard Bellows listed above with the addition of TRU-FLEX’s patented torsional joint. The Torsional Bellows line of flexible metal exhaust hoses is the ideal solution for a decoupler that will accommodate a full range of motion, including torsion or twisting motion. The torsional joint is, for all intents and purposes, a sealed slip joint and allows for the ends to rotate relative to each other. Some customers use this feature to ease assembly of the exhaust system.


TRU-FLEX's Unlined Torsional Bellows offers extremely long fatigue life and is compliant with North American and European Emissions Standards.


  • Patented B/T Joint
  • Bellows Body
  • Variety of ends


Lined Torsional Bellows offers enhanced durability and the added benefit of noise reduction. This product has excellent thermal insulation properties, potentially eliminating the need for extra insulation. It also reduces static loss.


  • Patented B/T Joint
  • Bellows Body
  • Polylock Liner
  • Mesh Ring (optional)

Premium Lined (Interlock and Mesh Damping Material)

Insulated Torsional Bellows delivers enhanced durability and the added benefit of vibration damping within the exhaust system. This is an ideal de-coupler to be used in situations where high frequency vibrations exist.


  • Patented B/T Joint
  • Bellows Body
  • Polylock Liner
  • Mesh Ring (optional)
  • Ends (optional)

More Information Check it out Torsional Bellows in Action

Insulated Bellows

Insulated Bellows add insulation to the mix. Insulated bellows assemblies are intended to keep precious heat inside the exhaust stream. A number of low- and high-tech materials and application methods (blankets, socks, metal encapsulation, …) are available to be engineered into your solution.


  • Corrugated stainless steel body
  • Internal polylock liner
  • Vibration damping mesh (optional)
  • Straight and/or bent flange end fittings
  • Full coverage insulation
  • Silicone bellows exterior

Low Skin Temp Bellows

The Low Skin Temp Bellows are similar to the insulated bellows listed just above but they include an extra bellows made from reinforced silicone to keep the external temperature of the bellows down. Depending on application this can serve the purpose of human skin contact safety or the lowering of risk igniting materials (such as wheat chaff or cotton) which may otherwise come into contact with the hot surface of the metal bellows inside. Of course the layers of insulation also provide heat retention within the exhaust stream.


  • Corrugated stainless steel body
  • Internal polylock liner
  • Vibration damping mesh (optional)
  • Straight and/or bent flange end fittings
  • Full coverage insulation
  • Silicone bellows exterior

Insulated Rigid Tubes

Insulated Rigid Tubes are a special product where the bellows are found inside a rigid tube and DO NOT provide vibration isolation such as traditional bellows but do afford the enablement of internal insulation or air gap within complex rigid tube assemblies.

Complex Assemblies

It is what it sounds like. Our most complex flexible assemblies can be made from many or all of the products features listed in one or multiple bellows in an assembly which includes multiple straight and bent sections of pipe and other features for mating to other exhaust components or attaching the assembly to a chassis.

Product Summary

The following table summarize the features available as standard or optional in the above products. With few exceptions all of these features can be combined in a myriad of ways. We suggest you engage with your Sales Engineer to discuss what is the best solution fitting your needs.

Corrugation Polylock Lining Braided Cover Torsional Joint Mesh Rings Insulation Silicone Bellows Cover End Features / Bends / Brackets Locally Reduced Bellows Special Alloys
Severe Duty
Low Skin Temp
Rigid Tube
Key: Standard Optional


Features and Benefits of Bellows

There are 8 feature categories which can be combined in many many ways to achieve the benefits our customers need to solve their challenges. The following table illustrates a summary of the key features (columns) and benefits (rows).

Corrugation Polylock Lining Braided Cover Torsional Joint Mesh Rings Insulation Silicone Bellows Cover End Features / Bends / Brackets Locally Reduced Bellows Special Alloys

Sales and Application Engineering

TRU-FLEX attracts customers from around the world. The reason? The superior sales and application engineering support and willingness to provide customer-specific solutions.

We have excellent sales and application engineers, with a deep experience in the industries that we serve. We design and manufacture flexible elements and fittings for exhaust systems to meet the performance requirements of our customers’ applications. Unlike some of our competitors, we are not afraid of custom applications. In fact, TRU-FLEX excels at providing customized solutions to exhaust system problems. Customers are encouraged to engage our team early in the process so that we can deliver the added value for which our company is known.

Data acquisition is one of our keys to success. Our technical sales organization has the knowledge and tools to gather extensive operational data from your prototype or development mule equipment. Often termed Road Load Data Acquisition (RLDA for short) our team combines high speed displacement data acquisition and high speed camera work to best understand the vibration isolation needs within your system.

Because we care so much about your successful application and use of our products we extend our technical support to what we call “Customer Coaching Seminars.” When it comes to flexible metal hose for exhaust systems TRU-FLEX is the expert and we are not shy about it. That is why we offer customer coaching seminars at your locations to help you maximize your likelihood of successful design, application and use. Those who would benefit from our coaching seminars include your executive, supervisory, and front-line employees—anyone with a vested interest in the success of your organization.

Design and Validation Testing

TRU-FLEX maintains extensive engineering and technical resources that are available to address the unique design verification and testing requirements of our customers. To support these efforts, we have created a proprietary design verification software to validate the calculated life of our parts over the life cycle of your product or application. This, coupled with our testing services, helps to ensure optimum performance post commercialization. These services can also be utilized to troubleshoot issues in existing applications.

Prototypes and Samples

Want a Sample of one of our products similar to what you are thinking about?

Give our sales team a call and they can sell you an existing ‘generic’ (non-customer-proprietary) part from our production which may be an approximate match to your needs. REMEMBER just about every customer has unique needs and TRU-FLEX never limits your solution to “off-the-shelf” so a sample will only get you into the ballpark. If you need an exact match consider ordering a prototype instead of a sample.

Need one or a small handful of custom-designed and made prototypes which exactly match your product development cycle? Call on our Sales and Application Engineering team to engage with you in a process to determine your needs, design a product which exactly fits these needs and then can deliver prototypes in support of your product development. Of course the proof of the pudding is in the tasting so we would not end there. After your prototype is in place our team will work with you to identify possible improvements, variants, iterations to the design and then work with you in a transition to production.

Product Research and Development

TRU-FLEX holds many patents and utilizes many proprietary methods for design and production of leading edge flexible exhaust products. We are not going to announce to the world on our web site what is going on in our skunk works. Instead we want to use this space to encourage you to bring your challenges to us and let our R&D team lead the way to the next generation of flexible exhaust solutions.

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Opportunity Starts Here

Opportunities don’t just happen. They are made. Let us know what you’re thinking, what you need, and where you’d like to go. We are there!

  • TRU-FLEX Exhaust Bellows
  • 2390 IN-263
  • West Lebanon, IN 47991
  • 800-255-6291
  • 765-893-4403

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