Polyurethane and rubber are both widely used in sealing applications, but they offer different performance characteristics. Polyurethane is often considered for applications requiring good wear resistance and mechanical strength, while rubber materials are available in a range of formulations for different sealing requirements, fluids, and temperatures.

Neither material is universally better. The right choice depends on the seal's function, hydraulic fluid, operating temperature, pressure, movement, and installation conditions.

Understanding Polyurethane and Rubber Seal Materials

1. What Are Polyurethane Seals?

Polyurethane seals are made from polyurethane elastomers, which combine elastic properties with good mechanical strength. They are commonly used in hydraulic cylinders and other applications involving repeated movement and contact with mating surfaces.

Depending on the formulation and seal design, polyurethane can offer:

• Good abrasion and wear resistance.
• Good resistance to tearing and mechanical damage.
• Useful resistance to extrusion under suitable operating conditions.
• Good sealing performance in many hydraulic applications.

Voneseals TecThane® Polyurethane Materials

At Voneseals, we go beyond standard polyurethane materials with our proprietary TecThane® Polyurethane Materials, developed through our in-house material research and engineering capabilities. Designed for demanding hydraulic and industrial sealing applications, TecThane® combines wear resistance, mechanical strength, and long-term durability to help improve sealing performance and extend equipment service life.

The TecThane® material platform includes different formulations tailored to specific operating requirements. Depending on the grade, these materials can provide enhanced hydrolysis resistance, improved performance in low-temperature environments, resistance to high-temperature hydraulic oil degradation, or high resilience for fast reciprocating and vibration-intensive applications.

Polyurethane is frequently used for hydraulic rod seals, piston seals, and wiper seals. However, performance varies between polyurethane formulations. Compatibility with hydraulic fluids, temperature limits, and resistance to hydrolysis should be evaluated for the specific material.

Explore our TecThane® polyurethane materials to learn more about our material grades and their application characteristics.

2.What Are Rubber Seals?

Rubber seals are made from elastomeric materials that can deform under load and recover their shape when the load is removed. This elasticity helps maintain contact with sealing surfaces and accommodate certain dimensional variations.

However, rubber is not a single material. Different rubber compounds have different chemical and physical properties.

Common rubber materials used in sealing applications include:

• NBR (nitrile rubber): Commonly used in applications involving compatible mineral oils and lubricants.
• FKM (fluoroelastomer): Often selected for applications requiring higher temperature resistance or compatibility with particular chemicals and fluids.
• VMQ (silicone rubber): Offers excellent temperature flexibility and weather resistance; suitable for air, water, and some compatible fluids, but generally not recommended for petroleum-based hydraulic oils.

The suitability of each material depends on its specific formulation and the operating environment.

Polyurethane vs. Rubber: Key Performance Differences

Polyurethane and rubber should be compared according to the requirements of the application rather than by material name alone.

1.Wear Resistance and Mechanical Strength

Wear resistance is an important consideration in dynamic hydraulic sealing applications. Seals used in reciprocating cylinders repeatedly contact moving surfaces, making them susceptible to friction and wear.

Polyurethane seals generally offer better abrasion resistance and mechanical strength than conventional rubber seals, making them well suited for hydraulic rod and piston seals.

Polyurethane resists repeated friction against metal surfaces, helping reduce material loss and maintain its sealing edge during continuous reciprocating movement. Its high tear strength also helps prevent damage caused by friction, pressure, and contact with surface imperfections. These properties help polyurethane seals maintain their shape, resist wear-related leakage, and achieve a longer service life in demanding hydraulic systems.

2.Elasticity and Sealing Contact

Rubber generally offers better elasticity and flexibility than polyurethane, making it suitable for applications that require repeated deformation and elastic recovery.

Its ability to stretch, compress, and return to its original shape helps maintain sealing contact as operating conditions change. This makes rubber a common choice for O-rings, static seals, and applications requiring reliable sealing under compression.

Polyurethane also provides good elasticity, but it is generally stiffer and less flexible than rubber, making it more suitable for applications where wear resistance and mechanical strength are key priorities.

3.Resistance to Hydraulic Fluids

Fluid compatibility is one of the most important factors in hydraulic seal selection.

A material that performs well mechanically may deteriorate if it is exposed to an incompatible fluid. Swelling, hardening, softening, or loss of mechanical properties can affect sealing performance.

NBR is commonly used with compatible mineral-oil-based hydraulic fluids. Certain polyurethane formulations are also suitable for many hydraulic oils, while FKM may be considered for some applications involving elevated temperatures or particular fluid requirements.

However, compatibility should not be assumed based on the material name alone. Hydraulic fluid formulation, additives, temperature, and exposure duration can all influence performance.

When Should You Choose Polyurethane Seals?

Polyurethane is often a suitable candidate when a hydraulic application places significant demands on wear resistance and mechanical strength.

Consider polyurethane seals when:

• The seal operates under repeated reciprocating movement.
• Wear resistance is an important requirement.
• The application requires good resistance to tearing or mechanical damage.
• The selected polyurethane grade is compatible with the hydraulic fluid and operating temperature.
• The seal geometry and installation conditions are suitable for the expected pressure and extrusion gap.

For example, a hydraulic cylinder operating frequently in industrial machinery may benefit from a polyurethane rod seal designed for its pressure, speed, fluid, and temperature conditions.

The same material should not automatically be specified for every seal position in that cylinder. Rod seals, piston seals, and wiper seals perform different functions and may require different material properties and designs.

You can explore our Hydraulic Rod Seals and Hydraulic Piston Seals to learn more about these sealing applications.

When Should You Choose Rubber Seals?

Rubber materials remain important in hydraulic and industrial sealing because different elastomers can meet a wide range of sealing requirements.

Rubber may be a suitable choice when:

• Elastic recovery is a key requirement for the seal design.
• The application uses an O-ring or another seal design commonly made from rubber.
• A specific rubber compound offers the required fluid compatibility.
• The operating temperature falls within the material's qualified range.
• The application requires properties that are better matched by a particular rubber formulation.

For example, NBR is frequently used for O-rings exposed to compatible mineral oils. FKM may be considered when the application requires resistance to higher temperatures or particular chemicals. VMQ is suitable for applications involving air, water, and certain oils, depending on the specific formulation.

These examples are not interchangeable recommendations. Each material has limitations, and the correct choice depends on the actual operating conditions.

How to Choose the Right Material for Hydraulic Seals?

Selecting a hydraulic seal material requires more than comparing a list of material properties. The seal must work as part of a complete sealing system.

Step 1: Identify the Sealing Function

First, determine where the seal will be installed and what it needs to do.

• Rod seals prevent hydraulic fluid from leaking along the piston rod.
• Piston seals limit fluid bypass between the two pressure chambers of a cylinder.
• Wiper seals remove contaminants from the piston rod as it retracts.
• O-rings are commonly used for static sealing and certain appropriately designed dynamic applications.

Different sealing positions have different requirements. Material selection should account for the function, seal profile, and installation location.

Step 2: Check the Hydraulic Fluid

Identify the exact hydraulic fluid or other medium that will contact the seal.

Check the material manufacturer's compatibility data, especially when the system uses specialized fluids, water-based hydraulic fluids, or fluids containing particular additives.

Do not assume that two materials are compatible with the same fluids simply because both are commonly used in hydraulic equipment.

Step 3: Confirm the Operating Temperature

Consider both the normal operating temperature and any temperature peaks.

Temperature can affect hardness, elasticity, wear, and chemical compatibility. A material that performs well at room temperature may behave differently at elevated or low temperatures.

Always verify the recommended operating range for the specific material grade.

Step 4: Evaluate Pressure and Movement

Determine the operating pressure, pressure peaks, movement speed, and whether the seal is exposed to reciprocating or rotary motion.

Pressure alone does not determine seal performance. Seal geometry, extrusion clearance, mating-surface condition, and supporting components also influence whether a sealing system can operate reliably.

For higher-pressure applications, confirm that the complete seal design is suitable for the specified conditions.

Step 5: Check Dimensions and Installation Conditions

Even a suitable material can fail if the seal is incorrectly sized or installed.

Before selecting a replacement, confirm:

• Shaft or bore diameter and groove dimensions.
• Seal profile and installation direction.
• Required hardness and dimensional tolerances.
• Surface finish and condition of the mating components.
• Installation tools and procedures.

If a seal repeatedly fails, investigate the cause before simply switching materials. Incorrect dimensions, contamination, misalignment, excessive clearance, and damaged mating surfaces may contribute to the problem.

Not sure which sealing material or product is right for your application? Contact us for expert guidance and customized sealing solutions.

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Can You Replace a Rubber Seal with a Polyurethane Seal?

In some applications, replacing a rubber seal with a polyurethane seal may be possible. However, matching the dimensions alone does not guarantee that the replacement will work correctly.

Before making the change, check the following:

• Material compatibility: Is the polyurethane grade compatible with the hydraulic fluid and temperature?
• Seal design: Is the profile suitable for the same sealing position and movement?
• Groove dimensions: Does the replacement fit the existing housing and provide the required sealing contact?
• Operating conditions: Can the replacement handle the pressure, speed, and extrusion clearance?
• Installation: Can the seal be installed without damaging the sealing lip or changing its intended geometry?

A material change should be based on engineering requirements rather than the assumption that polyurethane is always more durable than rubber.

If an existing seal fails prematurely, identifying the failure mechanism can be more useful than changing the material immediately.

FAQ

Are polyurethane seals more dependable than rubber seals?

In the majority of abrasive, high-pressure, or high-cycle processes Yes, polyurethane's higher abrasion and extrusion resistance generally means it has an extended service life than conventional rubber compounds in the circumstances.

When should I choose rubber seals over polyurethane for my hydraulic system?

Rubber seals, especially Nitrile Rubber Seals, are best chosen for low-pressure, cost-sensitive systems where flexibility matters more than wear resistance. They work well in moderate temperatures and less demanding hydraulic applications.

Can polyurethane and rubber be used in the same hydraulic cylinder?

Yes. A hydraulic cylinder can use different materials for different sealing positions. For example, polyurethane may be selected for a dynamic rod seal while an appropriately specified rubber compound is used for an O-ring. Each component should be selected according to its own requirements and compatibility conditions.

Conclusion: Choosing the Right Seal for Long-Term Hydraulic Performance

Choosing between rubber and polyurethane seals depends on the operating temperature, pressure, and specific requirements of the hydraulic system. Polyurethane seals are often preferred for heavy-duty applications due to their excellent wear resistance and durability, while rubber seals can be a suitable option for applications where cost and specific material properties are key considerations. To extend seal service life and reduce the frequency of replacements, it is important to select a seal material that matches the operating conditions and performance requirements of the system.