Designing a custom rubber extrusion involves much more than creating the shape of the profile.
Material selection, durometer, compression, tolerances, wall thickness, operating environment, and secondary operations can all influence whether the finished extrusion performs as intended.
Making these decisions early in the design process can help reduce manufacturing challenges, improve product performance, and potentially avoid costly changes after tooling or production has begun.
Northwest Rubber Extruders (NWRE) manufactures custom rubber extrusions for a wide variety of OEM and industrial applications. If you’re developing a new extruded rubber component, here are eight important factors to consider before finalizing your design.
1. Define the Operating Environment
Before selecting a rubber material or finalizing a profile, determine exactly where the component will be used.
The operating environment can have a significant effect on rubber performance.
Important questions include:
- What is the maximum operating temperature?
- What is the minimum operating temperature?
- Will the component be installed indoors or outdoors?
- Will it be exposed to sunlight?
- Will it encounter ozone?
- Will it be exposed to water or moisture?
- Will it encounter oils or fuels?
- Are chemicals or cleaning agents present?
- Will the component experience abrasion?
- Is vibration present?
- Will the extrusion remain continuously compressed?
The answers help determine which elastomer and profile design should be considered.
For example, EPDM is frequently used for outdoor applications because of its resistance to weather, ozone, water, and UV exposure.
Nitrile, on the other hand, is commonly considered when petroleum-based oil resistance is important.
For applications involving demanding temperature conditions, silicone extrusions may also be appropriate.
Start with the environment—not the material.
Once you understand what the extrusion needs to withstand, you can begin narrowing down the available compounds.
2. Choose the Right Rubber Material
There is no single rubber material that is ideal for every application.
Different elastomers provide different performance characteristics.
Some commonly used materials include:
EPDM
EPDM is widely used for applications requiring resistance to:
- Weather
- Ozone
- Water
- UV exposure
- Environmental aging
This makes it particularly useful for outdoor seals, construction products, transportation components, and HVAC applications.
Neoprene
Neoprene provides balanced performance across several categories.
It offers good resistance to weathering and abrasion along with moderate resistance to certain oils.
This versatility makes it useful for many general industrial applications.
Nitrile
Nitrile, also known as Buna-N or NBR, is particularly valued for its resistance to petroleum-based oils and fuels.
It may be considered for machinery, automotive, hydraulic, and industrial applications.
SBR
SBR is a general-purpose synthetic rubber that can provide useful abrasion resistance and mechanical properties.
It may be appropriate for applications that don’t require specialized environmental or chemical resistance.
Silicone
Silicone is often considered when an application requires performance across a demanding temperature range or excellent resistance to environmental aging.
NWRE’s Material & Engineering resources provide additional information related to material selection.
3. Determine the Correct Durometer
After selecting the general material, engineers should consider durometer.
Durometer is a measure of rubber hardness.
A softer rubber compound generally compresses more easily, while a harder compound is more resistant to deformation.
This can have a major impact on how an extrusion performs.
For example, a door seal may need enough flexibility to compress when the door closes.
If the rubber is too hard, excessive closing force may be required.
On the other hand, an industrial bumper may require a harder compound to provide sufficient resistance to impact and deformation.
The appropriate durometer depends on factors such as:
- Compression requirements
- Sealing pressure
- Profile geometry
- Mechanical load
- Installation method
- Flexibility
- Wear resistance
Durometer should therefore be considered together with profile design rather than treated as a separate decision.
4. Design the Profile Around Its Function
The cross-sectional shape of a custom extrusion has a direct impact on performance.
A profile may need to:
- Create a seal
- Fill a gap
- Absorb impact
- Reduce vibration
- Protect an edge
- Provide cushioning
- Isolate two components
- Resist movement
- Create a barrier against water or air
Different functions require different geometries.
Common extrusion profiles include:
- D-shaped profiles
- P-shaped profiles
- U-channels
- Tubing
- Rubber strips
- Hollow seals
- Solid seals
- Bulb profiles
- Custom geometric shapes
A simple profile is often preferable when it can meet the application’s requirements.
Unnecessary complexity can potentially increase tooling difficulty and make dimensional control more challenging.
However, certain applications require more complex shapes to achieve the desired compression or installation characteristics.
The goal should be to create the simplest profile capable of reliably performing the required function.
5. Consider Solid vs. Hollow Profiles
Another important design decision is whether the extrusion should be solid or hollow.
Solid Rubber Profiles
Solid profiles can provide greater resistance to deformation and may be useful for:
- Bumpers
- Spacers
- Protective strips
- Wear surfaces
- Edge protection
- Certain gaskets and seals
Because the material is solid throughout the cross section, these profiles generally require greater force to compress.
Hollow Rubber Profiles
Hollow profiles contain an internal cavity that allows the extrusion to deform more easily under pressure.
This can be particularly useful for sealing applications.
Common examples include:
- Door seals
- Hatch seals
- Enclosure seals
- Automotive seals
- Equipment seals
A hollow profile can sometimes provide the desired sealing pressure without requiring an extremely soft rubber compound.
This illustrates why material selection and profile geometry should be evaluated together.
6. Establish Realistic Tolerances
Tolerances are extremely important when designing a custom rubber extrusion.
However, rubber doesn’t behave like machined metal.
Elastomeric materials are flexible and can change dimensions during extrusion, curing, cooling, and handling.
The geometry of the profile can also influence how easily dimensions can be controlled.
Engineers should therefore distinguish between:
Critical dimensions — dimensions that directly affect fit or performance.
and
Non-critical dimensions — dimensions where slightly more variation will not affect the finished assembly.
Applying unnecessarily tight tolerances to every dimension can make manufacturing more difficult without improving the finished product.
Instead, focus tighter requirements on dimensions that truly affect:
- Fit
- Compression
- Installation
- Sealing
- Alignment
- Product performance
Discussing critical tolerances with the manufacturer before tooling can help identify potential production challenges early.
7. Think About Compression and Sealing
If the extrusion is being used as a seal, compression should be considered during the initial design process.
A rubber seal typically needs to compress enough to maintain contact between two mating surfaces.
Too little compression can result in inadequate sealing.
Too much compression can potentially:
- Increase closing force
- Stress surrounding hardware
- Permanently deform the rubber
- Reduce service life
The appropriate compression depends on the material, durometer, profile geometry, and application.
Compression Set
Another consideration is compression set.
Compression set refers to a rubber material’s tendency to remain permanently deformed after being compressed for an extended period.
Imagine an equipment door that remains closed most of the time.
The rubber gasket around that door may remain compressed for weeks or months.
When the door opens, the extrusion should ideally recover enough to continue creating an effective seal when the door is closed again.
Material selection and profile design can influence this behavior.
Applications involving continuous compression should therefore be evaluated carefully.
8. Plan for Secondary Operations
The extrusion process may create the basic profile, but many components require additional work before they’re ready for installation.
These are commonly referred to as secondary or value-added operations.
Depending on the project, they may include:
- Cutting to specific lengths
- Splicing
- Joining
- Adhesive application
- Fabrication
- Packaging
- Other finishing operations
Thinking about these requirements during the design phase can help simplify manufacturing later.
For example, if an extrusion ultimately needs to be cut into thousands of identical pieces, it may make sense to incorporate that requirement into the production plan rather than treating it as a separate process after manufacturing.
Similarly, if adhesive backing is required for installation, surface geometry and material compatibility may need to be considered.
Bonus Consideration: Installation
A rubber extrusion can perform perfectly in testing but still create problems if it is difficult to install.
Think about how the component will actually be assembled.
Will it:
- Slide into a channel?
- Press into a groove?
- Attach using adhesive?
- Fit over an edge?
- Be mechanically fastened?
- Be compressed between two components?
Installation requirements can influence the profile geometry and material hardness.
For example, a profile designed to slide through a narrow channel may require different dimensional considerations than a seal that is simply pressed into place.
For high-volume manufacturing, installation time can also become an important cost consideration.
A small profile change that saves several seconds during assembly can become significant when thousands of components are produced.
Designing for the Application, Not Just the Drawing
One of the most important principles in custom rubber extrusion design is to think beyond the drawing itself.
A drawing defines dimensions, but it doesn’t always communicate the full operating environment.
Manufacturers benefit from understanding what the extrusion actually needs to do.
For example:
A profile described simply as an “EPDM seal” doesn’t explain whether it will be installed outdoors, continuously compressed, exposed to water, or expected to operate for many years.
Providing information about the actual application can help identify potential material or manufacturing considerations before production begins.
NWRE works with customers across a variety of industries and applications, each with different environmental and performance requirements.
Information to Provide When Requesting a Custom Extrusion Quote
Providing detailed information at the beginning of a project can make the quoting process more efficient.
Whenever possible, provide:
A Drawing
A dimensional drawing is one of the most useful pieces of information.
Include the cross-sectional geometry and identify critical dimensions.
Material Requirements
Specify the elastomer if it has already been selected.
If the material hasn’t been determined, provide information about the operating environment.
Durometer
Include the required hardness when known.
Tolerances
Identify dimensions that are critical to fit and performance.
Quantity
Provide expected order quantities or annual production requirements.
Length
Specify whether the extrusion will be supplied in continuous lengths, coils, or individual cut pieces.
Environmental Requirements
Identify exposure to:
- Temperature
- Weather
- UV
- Ozone
- Water
- Oil
- Fuel
- Chemicals
- Abrasion
Secondary Operations
Include requirements for cutting, joining, adhesive, fabrication, or other finishing processes.
The more information available at the beginning of the project, the easier it is to evaluate manufacturing requirements.
Common Mistakes to Avoid When Designing Rubber Extrusions
Several issues can create unnecessary complications during product development.
Selecting Material Based Only on Cost
The least expensive material isn’t necessarily the most economical solution if it fails prematurely in the application.
Specifying Unnecessarily Tight Tolerances
Rubber extrusion tolerances should reflect the actual functional requirements of the part.
Ignoring Compression
A seal should be designed around the amount of available compression.
Focusing Only on Maximum Temperature
Minimum temperatures and environmental exposure can be equally important.
Forgetting About Installation
The profile needs to work not only after installation but during the assembly process.
Waiting Until Tooling to Discuss Manufacturing
Manufacturing considerations are easier to address before tooling has been created.
From Design to Production
A successful custom rubber extrusion requires several decisions to work together.
The material must withstand the environment.
The durometer needs to provide the appropriate flexibility.
The profile needs to create the desired seal or mechanical function.
The tolerances need to support the finished assembly while remaining practical for rubber manufacturing.
And secondary operations should be considered before production begins.
Taking a complete approach to extrusion design can help improve performance while reducing unnecessary manufacturing complications.
Work With Northwest Rubber Extruders
Northwest Rubber Extruders manufactures custom rubber, silicone, and flexible plastic extrusions for customers across a broad range of industries.
Whether you’re designing a new component or looking to manufacture an existing profile, NWRE can work from customer drawings and specifications to produce custom extruded products.
Learn more about our Rubber Extrusions, Silicone Extrusions, Material & Engineering, and Industries Served capabilities.
Have a drawing or specification ready for review? Request a Quote from Northwest Rubber Extruders.