Isolast J9504 vs Kalrez 4079: FFKM Compound Comparison
Verified by Rachel Mayfield, Supply Chain Analyst - April 2026
Isolast J9504 and Kalrez 4079 are both perfluoroelastomer (FFKM) compounds used in chemical, refinery, and process applications. Isolast J9504 vs Kalrez 4079 They share similar chemistry but differ on temperature ceiling, hardness, and intended service. This page compares the two side-by-side and explains when to specify each.
Side-by-side comparison
| Property | Isolast J9504 | Kalrez 4079 |
|---|---|---|
| Manufacturer | Trelleborg Sealing Solutions | DuPont (Chemours) |
| Compound | J9504 | 4079 |
| Maximum continuous temp | 270°C | 316°C |
| Minimum temp | -10°C | 0°C |
| Hardness | 75 Shore A | 75 Shore A |
| Colour | Black | Black |
| Typical applications | Refinery, chemical, hot service | Steam, hot amines, ethylene oxide, sour gas, refinery valves, pulp and paper digesters |
When to specify Isolast J9504
Isolast J9504 suits refinery and similar service. Continuous temperature window is -10°C to 270°C, hardness 75 Shore A. Manufactured by Trelleborg Sealing Solutions.
When to specify Kalrez 4079
Kalrez 4079 suits steam and similar service. Continuous temperature window is 0°C to 316°C, hardness 75 Shore A. Manufactured by DuPont (Chemours).
Limitation: Not recommended for fully fluorinated solvents; cost.
Key differences
- Temperature ceiling: Kalrez 4079 runs 46°C hotter (316°C vs 270°C). Specify the higher-rated compound when continuous service is above 270°C.
- Hardness: Both are 75 Shore A, so groove design and squeeze percentage are interchangeable.
- Manufacturer: Isolast J9504 is from Trelleborg Sealing Solutions; Kalrez 4079 is from DuPont (Chemours). Lead time and UK availability vary by brand.
- Cost: FFKM pricing varies by manufacturer, batch size, and stock position. Both compounds are at the premium end of elastomer pricing (£30 to £500+ per O-ring depending on size).
Get a UK quote on either compound
Related pages
- Isolast J9504 compound details
- Kalrez 4079 compound details
- BS 1806 O-ring size chart
- ISO 3601 metric O-ring sizes
References
- Trelleborg Sealing Solutions — Isolast J9504
- DuPont (Chemours) — Kalrez 4079
- BS 1806
- ISO 3601
Frequently Asked Questions
Can I substitute Isolast J9504 for Kalrez 4079?
Yes, Isolast J9504 and Kalrez 4079 are both FFKM compounds with overlapping chemical compatibility. Verify your specific fluid against both manufacturers' compatibility tables before substitution. Temperature window, hardness, and certifications may differ.
Which is hotter: Isolast J9504 or Kalrez 4079?
Kalrez 4079 has a higher continuous temperature ceiling (316°C vs 270°C, a 46°C difference).
Which costs less: Isolast J9504 or Kalrez 4079?
FFKM compound pricing depends on manufacturer, batch size, certifications, and current stock position rather than headline brand. Both compounds are at the premium end of elastomer pricing. Get current UK quotes on both before specifying.
Where can I buy Isolast J9504 or Kalrez 4079 in the UK?
Both compounds are supplied in the UK by independent FFKM seal specialists carrying multiple manufacturer lines. Lead time is typically 2-5 working days for stock BS 1806 / AS568 sizes, 4-8 weeks for custom-moulded sizes.
References
- Trelleborg Sealing Solutions — Isolast J9504
- DuPont (Chemours) — Kalrez 4079
- BS 1806
- ISO 3601