Introduction: Why Is Kalrez® 6375 So Frequently Searched?
When sealing materials fail, the consequences can be severe: corrosive fluid leaks, product contamination, or costly unplanned downtime. This is why engineers and procurement specialists often search terms like “Kalrez vs Chemraz”, “FFKM vs PTFE”, or “O-ring chemical compatibility”.
The underlying challenge is clear: finding a sealing solution that maintains long-term reliability in environments involving high temperatures, aggressive acids and bases, and mixed chemical streams.
Among the available options, Kalrez® Spectrum™ 6375 is often regarded as one of the most comprehensive solutions. Drawing on DuPont’s published technical data, we’ve compiled a structured overview to help you understand how it compares with alternatives.
Trademark Notice
The product names mentioned in this article are registered trademarks of their respective owners:
Kalrez® is a registered trademark of DuPont de Nemours, Inc.
Chemraz® is a registered trademark of Greene Tweed & Co.
Simriz® is a registered trademark of Freudenberg Sealing Technologies
PTFE refers to polytetrafluoroethylene, a generic polymer name, while Teflon® is a registered trademark of The Chemours Company FC, LLC.
This article is based solely on publicly available data and technical documentation. All rights remain with the respective trademark holders.
1. Product Positioning and Technical Background
Kalrez® Spectrum™ 6375 is an FFKM (perfluoroelastomer) product developed by DuPont®. The nearly fully fluorinated molecular structure gives it a rare combination: the chemical inertness of PTFE paired with the elasticity of a rubber material. This balance allows Kalrez seals to withstand aggressive chemical attack while retaining sealing force under high-temperature conditions.
Performance highlights:
- Maximum continuous service temperature: 275 °C (527 °F)
- Minimum service temperature: −20 °C (−4 °F)
- Chemical resistance: Excellent stability against sulfuric acid, nitric acid, acetic acid, urea, isocyanates, ethylene oxide, and more
- Target applications: Environments with mixed chemical exposure and thermal excursions
Compared with Chemraz® 505, Simriz® 495, or PTFE, Kalrez 6375 consistently delivers a stronger balance of chemical compatibility and compression set resistance, making it a highly recommended material for long-term critical sealing needs.
2. Key Properties (Datasheet Highlights)
From DuPont’s published datasheet, typical properties of Kalrez 6375 include:
| Property | Value | Test Method |
|---|---|---|
| Hardness | 75 Shore A | ASTM D2240 |
| Tensile strength | 15.1 MPa (2200 psi) | ASTM D412 |
| Elongation at break | 160% | ASTM D412 |
| Compression set | ~30% after 70 hr @ 204 °C | ASTM D395B / D1414 |
| Max. service temperature | 275 °C (527 °F) | DuPont method |
| Min. service temperature | −20 °C (−4 °F) | DuPont method |
These figures show how Kalrez 6375 strikes a balance between mechanical strength, elasticity, and thermal stability. Even under prolonged high-temperature operation, it maintains sealing force without excessive compression set.
3. Chemical Compatibility and Resistance
Laboratory testing highlights the chemical durability of Kalrez 6375:
- 98% sulfuric acid (150 °C): Rated A (<10% volume swell)
- 70% nitric acid (85 °C): Rated B (10–20% volume swell)
- Urea (175 °C): Rated A
- Ethylene oxide (50 °C): Rated A
In contrast, Chemraz tends to exhibit higher swell in nitric acid and urea environments, while Simriz shows limitations in prolonged exposure to hot mixed acid systems.
4. Kalrez vs. Chemraz vs. PTFE: Competitive Comparison
| Material | Temperature Range | Acid Resistance | Dynamic Sealing | Cost Effectiveness | Typical Use Cases |
|---|---|---|---|---|---|
| Kalrez 6375 | −20 ~ 275 °C | Excellent | Strong elasticity, low compression set | High upfront cost, lower TCO | Industrial sealing alternatives |
| Chemraz 505 | −15 ~ 260 °C | Good, less stable in hot acids | Moderate elasticity | Mid-to-high cost | Industrial sealing alternatives |
| Simriz 495 | −15 ~ 250 °C | Moderate | General | Medium cost | Industrial sealing alternatives |
| PTFE | −200 ~ 260 °C | Excellent (chemically inert) | No elasticity, only static use | Low cost | Static seals, cost-sensitive environments |
This comparison shows why Kalrez 6375 is considered superior in dynamic, high-temperature, and chemically aggressive applications, while PTFE remains valid for static sealing where elasticity is not required.
5. Frequently Asked Questions (FAQ)
Q1: What is the difference between FFKM and FKM?
Structure: FKM (fluoroelastomer) is partially fluorinated, while FFKM is almost fully fluorinated, which provides exceptional chemical stability.
Temperature range: FKM is generally suitable up to ~200 °C, whereas Kalrez 6375 is rated to 275 °C.
Chemical compatibility: FKM performs well in moderate acids, bases, and oils but degrades in concentrated sulfuric or nitric acid; FFKM maintains stability in these conditions.
Application choice: For environments involving high temperature plus aggressive chemicals, engineers typically prefer FFKM.
Q2: How long do FFKM O-rings last?
Key factors: Service life depends on temperature, pressure, chemical medium, and cycling frequency.
Compression set: Kalrez 6375 shows ~30% set after 70 hours at 204 °C, indicating strong resilience compared to standard FKM.
Relative durability: If an FKM O-ring requires monthly replacement under harsh conditions, FFKM O-rings based on datasheet performance may last several times longer.
Installation considerations: Seal life is also influenced by groove design and compression ratio—improper installation can shorten life, even for FFKM.
Q3: Can Kalrez 6375 replace PTFE?
Key factors: Service life depends on temperature, pressure, chemical medium, and cycling frequency.
Compression set: Kalrez 6375 shows ~30% set after 70 hours at 204 °C, indicating strong resilience compared to standard FKM.
Relative durability: If an FKM O-ring requires monthly replacement under harsh conditions, FFKM O-rings based on datasheet performance may last several times longer.
Installation considerations: Seal life is also influenced by groove design and compression ratio—improper installation can shorten life, even for FFKM.
Q4: Is Kalrez® 6375 suitable for CIP/SIP cleaning cycles?
Cleaning conditions: CIP (clean-in-place) and SIP (sterilize-in-place) often involve 120–140 °C steam and alkaline solutions.
Resistance: DuPont’s data confirms Kalrez 6375’s compatibility with hot water and steam, making it suitable for repeated cleaning cycles.
Comparison: Chemraz tends to show higher compression set after multiple cycles, while Kalrez maintains lower set and stronger long-term sealing performance.
Q5: Why is Kalrez® 6375 often listed as the “best elastomer for high-temperature seals”?
Temperature capability: Continuous service up to 275 °C places Kalrez® among the top-performing elastomers available.
Chemical breadth: It resists strong acids, bases, and many solvents simultaneously.
Performance balance: Its combination of thermal stability, chemical resistance, and elasticity makes it a go-to material for engineers specifying high-performance sealing solutions.
6. Conclusion
Kalrez® Spectrum™ 6375 represents one of the most comprehensive solutions currently available for chemical resistance and high-temperature sealing.
Although its upfront cost is higher than FKM or PTFE, its exceptional resistance to aggressive media, high-temperature resilience, and reliable compression set control make it a cost-effective choice over the long term. For industries where seal failure is not an option, Kalrez 6375 is often considered the standard.
If you’ve been searching for:
- “Kalrez vs Chemraz chemical resistance”
- “FFKM vs PTFE for high-temperature sealing”
- “How long do FFKM O-rings last”
- “Best elastomer for high-temperature seals”
—Kalrez Spectrum™ 6375 is likely to appear at the top of every recommendation list.
Selecting the right sealing material enhances equipment reliability, reduces maintenance costs, and safeguards production continuity. For more technical information, compatibility charts, or datasheet resources, refer to DuPont’s official documentation or visit our Resource page or Contact us for support.
