Chemraz 555 vs Kalrez 6375: FFKM Compound Comparison
Verified by Rachel Mayfield, Supply Chain Analyst - April 2026
Chemraz 555 and Kalrez 6375 are both perfluoroelastomer (FFKM) compounds used in chemical, refinery, and process applications. Chemraz 555 vs Kalrez 6375 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 | Chemraz 555 | Kalrez 6375 |
|---|---|---|
| Manufacturer | Greene Tweed | DuPont (Chemours) |
| Compound | 555 | 6375 |
| Maximum continuous temp | 240°C | 275°C |
| Minimum temp | -20°C | -7°C |
| Hardness | 75 Shore A | 75 Shore A |
| Colour | Black | Black |
| Typical applications | Pharmaceutical, chemical process | Chemical process, pharmaceutical, semiconductor wet etch, hot/cold cycling |
When to specify Chemraz 555
Chemraz 555 suits pharmaceutical and similar service. Continuous temperature window is -20°C to 240°C, hardness 75 Shore A. Manufactured by Greene Tweed.
When to specify Kalrez 6375
Kalrez 6375 suits chemical process and similar service. Continuous temperature window is -7°C to 275°C, hardness 75 Shore A. Manufactured by DuPont (Chemours).
Limitation: Lower temp ceiling than 4079; not for high-purity semiconductor plasma.
Key differences
- Temperature ceiling: Kalrez 6375 runs 35°C hotter (275°C vs 240°C). Specify the higher-rated compound when continuous service is above 240°C.
- Hardness: Both are 75 Shore A, so groove design and squeeze percentage are interchangeable.
- Manufacturer: Chemraz 555 is from Greene Tweed; Kalrez 6375 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
Frequently Asked Questions
Can I substitute Chemraz 555 for Kalrez 6375?
Yes, Chemraz 555 and Kalrez 6375 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: Chemraz 555 or Kalrez 6375?
Kalrez 6375 has a higher continuous temperature ceiling (275°C vs 240°C, a 35°C difference).
Which costs less: Chemraz 555 or Kalrez 6375?
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 Chemraz 555 or Kalrez 6375 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.