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Fabric Bellows
Fabric bellows expansion joints are lightweight, highly flexible connectors made from heat-resistant materials. Perfect for gas turbine exhausts, flue gas systems and HVAC applications, they absorb large multi-directional movements. Their construction allows for easy installation in areas with limited space or weight restrictions, while offering thermal, chemical, noise and vibration protection.
What Are Fabric Bellows?
A fabric bellows is a flexible expansion joint constructed from engineered, multi‑layer materials designed to provide:
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Flexibility to accommodate movement (axial/lateral/angular, often multi-directional);
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Sealing to contain gas flow (where required);
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Thermal protection suitable for hot gas duties;
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A practical solution for large ducting sections and rectangular transitions.
Bolster bags can also be used to provide extra protection from media, temperature and mechanical stresses or further noise reduction.
The following terms are often used interchangeably:
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Fabric bellows;
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Fabric expansion joints;
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Duct expansion joints;
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Flue expansion joints;
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Fabric duct bellows.
Fabric bellows are generally used in ducting and flue systems rather than pressurised pipework. For pressurised pipe systems, metallic solutions may be more appropriate (see Metal Expansion Joints).
Where Fabric Bellows Are Typically Used
Fabric bellows are commonly specified in:
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Power generation and CHP, flue gas ducts, boiler connections, air preheater ducting, exhaust runs;
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Energy-from-waste and thermal systems: hot gas handling ductwork and flue transitions;
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Industrial process plants: hot air ducts, fume extraction, ventilation and process gas systems;
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Large HVAC and industrial air handling: where movement must be absorbed without stressing ductwork.
Fabric bellows are especially valuable where duct sizes are large and a metallic solution would be heavier, less flexible or more difficult to fit within the envelope.
Types & Configurations Of Fabric Bellows
Fabric bellows are engineered to suit your duct geometry and movement pattern.
Common configuration variables include:
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Rectangular fabric bellows for ducting and flues (the most common format);
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Circular fabric bellows (where the duct is round);
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Single-bellows or multi-bellows arrangements depending on movement and envelope;
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Frame styles and interfaces to suit your mating ductwork (angles, flanges, custom frames);
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Installation methods designed for maintainability (clamping arrangements, bolting access).
If your application is specifically rectangular ducting, you may also want to reference our Rectangular Bellows page for geometry-led considerations.
Key Design Considerations (What Drives Reliability)
Fabric bellows performance depends on matching the design to the duty profile. Key considerations include:
Temperature, Thermal Cycling and Insulation Strategy:
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Continuous temperature and peak temperature;
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Thermal cycling frequency and transients;
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Whether insulation and external lagging are present and how they affect joint temperature profile.
Pressure and System Loads:
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Even 'low pressure' ducting can impose significant loads on a joint - fabric joints are not advised for high pressure;
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Pressure fluctuations and pulsation can greatly affect fatigue performance;
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Frame design and joint sizing must match pressure class and structural loads.
Movement Pattern and Directionality:
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Required axial/lateral/angular movement and whether movement is multi-directional;
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Duct growth behaviour (large ducting can move in complex ways);
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Ensuring the joint is not forced into an unintended shape during operation.
Flow Conditions and Particulates:
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Gas velocity and turbulence;
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Particulate content that may cause erosion or abrasion;
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Whether internal protection is required to reduce wear.
Environment and Exposure:
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Outdoor exposure (UV, weathering) and industrial contamination;
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Marine exposure where corrosion-resistant frames and hardware are needed;
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Mechanical damage risk during maintenance and shutdown work.
Many fabric bellows failures in the field trace back to mis-specified movement, unaccounted thermal growth, or installation constraints that prevent the joint from moving as intended.
Layered Construction & Materials (How It's Made)
Fabric expansion joints often use multi-layer construction tailored to duty, which may include:
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Gas-tight layers (where sealing is required);
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Thermal insulation layers to manage temperature at structural elements;
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Reinforcement layers to support movement and durability;
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External protective layers to resist weathering or contamination.
The correct material of layers depends on temperature, media, pressure, and expected movements and cycles. For harsh external exposure, protective features may be critical (see Any Environment Bellows for environment-led design factors).
Inspection, Testing & Documentation (As Specified)
Depending on project requirements, supply can be supported with:
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Installation guide;
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Verification of dimensions, interfaces and fit-up requirements;
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Documentation aligned to project needs (materials, construction, inspection records);
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Inspection approach suited to the installation and duty profile.
(Testing and documentation scope varies by project specification and application.)
How To Request A Quote (What We Need)
To quote for fabric bellows, please provide:
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Duct size (width × height for rectangular ducting) and drawings if available;
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Available envelope (overall length) for the bellows and frame hardware;
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Operating and maximum temperature (including thermal cycling details);
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Operating or design pressure (even if low) and any pressure fluctuations;
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Gas or media description (flue gas, hot air, exhaust) and particulate content;
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Required movement in each direction and expected cycles;
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Connection details (frame type, drilling and bolting details, mating duct specification);
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Any required documentation, standards, or inspection expectations.
Send drawings or specifications and we will recommend a fabric bellows construction and quote accordingly.
FAQs About 'Fabric Bellows'
Are fabric bellows the same as fabric expansion joints? Yes - these terms are commonly used interchangeably, especially for ducting and flue systems.
When should I choose a fabric bellows instead of a metallic expansion joint? Fabric bellows are typically chosen for ducting/flue systems at low pressure with high temperature and significant movement. Metallic expansion joints are more common in pressurised pipework systems or where a rigid engineered interface is required.
Can fabric bellows handle multi-directional movement? Yes, but the movement direction and magnitude must be defined so the bellows can be engineered and installed correctly.
Do fabric bellows work outdoors? Yes, but outdoor exposure affects material selection and protective layers, and may require suitable frame/hardware choices.
What’s the fastest way to get a quotation? Send duct drawings plus temperature, pressure and movement requirements. Photos of the existing installation can help for retrofit.
Read more FAQs here
