Chemraz 633 vs Kalrez 8475: FFKM Compound Comparison
Verified by Rachel Mayfield, Supply Chain Analyst - April 2026
Chemraz 633 and Kalrez 8475 are both perfluoroelastomer (FFKM) compounds used in chemical, refinery, and process applications. Chemraz 633 vs Kalrez 8475 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 633 | Kalrez 8475 |
|---|---|---|
| Manufacturer | Greene Tweed | DuPont (Chemours) |
| Compound | 633 | 8475 |
| Maximum continuous temp | 327°C | 325°C |
| Minimum temp | 0°C | 0°C |
| Hardness | 90 Shore A | 90 Shore A |
| Colour | Black | Black |
| Typical applications | Oil and gas, high-pressure valves | Oil and gas downhole, high-pressure valve seats, rapid gas decompression |
When to specify Chemraz 633
Chemraz 633 suits oil and gas and similar service. Continuous temperature window is 0°C to 327°C, hardness 90 Shore A. Manufactured by Greene Tweed.
When to specify Kalrez 8475
Kalrez 8475 suits oil and gas downhole and similar service. Continuous temperature window is 0°C to 325°C, hardness 90 Shore A. Manufactured by DuPont (Chemours).
Key differences
- Temperature ceiling: Chemraz 633 runs 2°C hotter (327°C vs 325°C). Specify the higher-rated compound when continuous service is above 325°C.
- Hardness: Both are 90 Shore A, so groove design and squeeze percentage are interchangeable.
- Manufacturer: Chemraz 633 is from Greene Tweed; Kalrez 8475 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 633 for Kalrez 8475?
Yes, Chemraz 633 and Kalrez 8475 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 633 or Kalrez 8475?
Chemraz 633 has a higher continuous temperature ceiling (327°C vs 325°C, a 2°C difference).
Which costs less: Chemraz 633 or Kalrez 8475?
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 633 or Kalrez 8475 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.