Basic comparison
| Material | General behaviour | Conditions for evaluation | Selection consideration |
|---|---|---|---|
| NBR | A widely used elastomer with an elastic structure and the ability to conform to the contact surface. | One of the common options that may be evaluated for standard sealing applications. | Fluid, temperature and hardness must be checked together with the material grade. |
| PU | Evaluated in applications requiring tear, wear and mechanical resistance. | May be evaluated in applications where mechanical load and wear behaviour are important. | Its recovery behaviour differs from that of elastomers; profile design is important. |
| FKM | An elastomer with specific grades offered for higher-temperature and special-fluid conditions. | May be evaluated for verified temperature or fluid conditions. | It should not be generalised that “FKM is suitable for every fluid.” |
| PTFE | Provides low friction and is available in different virgin and filled compositions. | May be evaluated in applications involving low friction, frequent motion or special fluid requirements. | Designs supported by an elastomer or spring may be required to maintain contact force. |
How do the materials differ?
NBR
NBR is one of the elastomers frequently used in sealing applications. Its elastic structure helps it conform to limited changes in the contact surface. Suitability cannot be determined from the name “NBR” alone; hardness, temperature class and fluid compatibility must be verified through the relevant grade code.
PU
PU-based materials are prominent in dynamic applications where wear, tearing and mechanical loads are important. Although their high mechanical properties offer advantages, the product profile, groove and contact conditions must be evaluated together because their recovery behaviour differs from that of elastomers.
FKM
FKM is an elastomer used in specific grades for higher-temperature conditions. However, not every FKM grade is suitable for every chemical or fluid. Fluid type, operating temperature and verified product data must be reviewed together.
PTFE
PTFE is evaluated in dynamic applications where low friction is important. Virgin PTFE and compounds filled with glass fibre, bronze, carbon-graphite or similar materials do not have identical properties. Because PTFE does not recover as readily as an elastomer, contact force in some profiles is supported by an elastomer or spring element.
Examples of Material Grades
The values below are not general limits for the material family; they are examples from the official material table for the specified grade codes only.
| Class | Grade code | Hardness | Specified temperature range |
|---|---|---|---|
| NBR | NB7001 | 70 Shore A | -30 / +105 °C |
| NBR | NB7012 | 70 Shore A | -50 / +105 °C |
| FKM | FK8001 | 80 Shore A | -25 / +200 °C |
| PU | PU9201 | 92 Shore A | -40 / +100 °C |
| PU | PU9411 | 94 Shore A | -35 / +120 °C |
| PTFE | PT5501 | 55 Shore D | -200 / +260 °C |
| PTFE | PT6003 | 60 Shore D | -200 / +260 °C |
Surface conformity behaviour
Frequently Asked Questions
Which seal material is better?
No single material is best for every application. Fluid, temperature, pressure, motion, surface and profile must be evaluated together.
What is the main difference between NBR and FKM?
Both are elastomers; specific FKM grades may be offered for higher-temperature conditions. Final selection must be based on the grade code and fluid compatibility.
Why may PTFE be supported by an elastomer or spring?
Although PTFE offers low friction, it may not recover as readily as elastomers. Profiles supported by an elastomer or spring may be used to maintain contact force.
Why does the material temperature range vary by grade code?
Different compositions and additives may exist within the same family. Values must therefore be read from the verified grade code.
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