Kalrez® vs. Viton™: Which Sealing Material Is Right for Your Application?

Choosing the right sealing material can make the difference between reliable equipment performance and premature seal failure. In demanding industrial applications, two materials that are frequently considered are Kalrez® perfluoroelastomer (FFKM) and Viton™ fluoroelastomer (FKM).

Both materials are designed to perform in environments where standard elastomers may not be suitable, but they are not interchangeable. Temperature, chemical exposure, operating conditions, service life and cost can all influence which material is the better choice.

Understanding the differences between Kalrez® and Viton™ can help you select the right sealing material for your application.

What Is Viton™ (FKM)?

Viton™ is a well-known brand of fluoroelastomer, commonly referred to as FKM. FKM materials are widely used for industrial seals and gaskets because they offer a strong combination of heat resistance, chemical resistance and durability.

Viton™ seals are commonly found in applications involving oils, fuels, lubricants, many acids and other aggressive fluids where conventional rubber materials may not provide sufficient resistance.

Depending on the specific compound and application, Viton™ can be used for:

• O-rings
• Custom gaskets
• Valve and pump seals
• Chemical processing equipment
• Oil and fuel systems
• Industrial piping and equipment

For many industrial applications, FKM provides an effective balance between performance and cost.

What Is Kalrez® (FFKM)?

Kalrez is a high-performance perfluoroelastomer, or FFKM, developed for extremely demanding sealing environments.

FFKM materials combine the elastic sealing properties associated with elastomers with exceptional resistance to a broad range of chemicals and high temperatures. This makes Kalrez® particularly valuable in applications where conventional elastomers, including many FKM compounds, may experience rapid degradation.

Kalrez seals are commonly used in demanding applications within industries such as:

• Chemical and petrochemical processing
• Oil and gas
• Semiconductor manufacturing
• Pharmaceutical processing
• Aerospace
• High-temperature industrial equipment
• Aggressive chemical handling systems

Different Kalrez compounds are engineered for different operating environments, making proper compound selection just as important as choosing FFKM itself.

Kalrez® vs. Viton™: What’s the Difference?

The primary difference between Kalrez® and Viton™ is their underlying elastomer chemistry.

Viton™ is an FKM material, while Kalrez® is an FFKM material. The additional fluorination of FFKM generally provides broader chemical resistance and the ability to perform under more severe operating conditions.

However, that additional performance comes at a significantly higher material cost.

The right choice should be based on the actual conditions of the application rather than simply selecting the highest-performance material available.

When Should You Use Viton?

Viton™ is often the better choice when an application requires strong chemical and temperature resistance but does not justify the additional cost of an FFKM material. For many industrial sealing applications, Viton™ provides more than enough performance. It may be a good option when the seal will encounter petroleum oils, fuels, lubricants, hydraulic fluids or certain chemicals, provided the specific FKM compound is compatible with the operating media and temperature.

Viton™ is also commonly selected when equipment requires reliable long-term sealing performance but operating conditions are not severe enough to require FFKM.

When Should You Use Kalrez®?

Kalrez® becomes particularly valuable when seal failure is expensive, dangerous or disruptive.

In severe chemical environments or applications involving elevated temperatures, an FKM seal may swell, harden, crack or otherwise deteriorate. Moving to an appropriate Kalrez® compound can provide substantially greater resistance under those conditions.

Kalrez® may be appropriate when:

• The application involves highly aggressive chemicals.
• Operating temperatures exceed the capabilities of the selected FKM compound.
• Frequent seal replacement is causing excessive equipment downtime.
• Contamination from seal degradation cannot be tolerated.
• Seal reliability is critical to process safety or production.
• A longer service interval could justify the higher initial material cost.

The question isn’t necessarily whether Kalrez® is a “better” material. The question is whether the application requires the additional capabilities of FFKM.

Is Kalrez® Worth the Higher Cost?

Kalrez® is considerably more expensive than Viton™, which makes cost an important part of the material-selection process.

Looking only at the purchase price of the gasket or seal, Viton™ will typically be the more economical option. But the cost of the seal itself isn’t always the largest expense.

Consider the total cost associated with a failure:

Seal Cost + Labor + Equipment Downtime + Lost Production + Cleanup + Potential Equipment Damage

If an inexpensive seal requires frequent replacement while a higher-performance FFKM seal can remain in service substantially longer, the more expensive material may ultimately provide a lower total operating cost.

For critical equipment, seal life and downtime should be considered alongside initial material price.

FFKM vs. FKM: Chemical Resistance Matters

Chemical compatibility is one of the most important considerations when comparing FFKM and FKM.

Both material families provide excellent chemical resistance compared with many conventional elastomers, but FFKM generally offers resistance across a broader range of aggressive media.

However, material family alone should never be used to determine compatibility.

The specific chemical, concentration, temperature, pressure and exposure conditions all matter. Different grades within the same material family can also behave differently.

For that reason, M&P recommends evaluating the complete operating environment before selecting a sealing material.

Don’t Overlook the Specific Compound

Choosing between Kalrez® and Viton™ is only the first step.

There are multiple grades and compounds within both material families. A compound designed for one environment may not be the best choice for another.

For example, M&P supplies a range of Kalrez® compounds for different chemical, temperature and processing requirements.

When selecting a material, consider:

• Operating temperature
• System pressure
• Chemical or process media
• Chemical concentration
• Static or dynamic service
• Required seal life
• Equipment and flange design
• Regulatory or cleanliness requirements

Providing this information when requesting a gasket or seal can help identify the most appropriate material for the application.

Kalrez® and Viton™ from M&P Sealing

M&P Sealing manufactures and supplies custom industrial gaskets and sealing solutions for demanding applications. With three in-house flash cutting systems, M&P can quickly manufacture custom gasket sizes and configurations from a wide range of sealing materials. In-house cutting capabilities also give our team greater flexibility when customers need prototypes, replacement gaskets, small quantities or expedited production.

Whether your application calls for Viton™/FKM, Kalrez®/FFKM, PTFE or another high-performance sealing material, our team can help evaluate your requirements and determine an appropriate solution. Need help choosing between Kalrez® and Viton™? Contact M&P Sealing with your operating temperature, pressure, media and gasket requirements, and our team can help you determine the right material for your application.