PTFE Creep

Why Does PTFE Creep and How Can You Prevent It?

PTFE is known for its excellent chemical resistance, low friction and wide operating temperature range. But it also has a limitation that engineers need to consider carefully: PTFE can creep under sustained load.

Creep is the gradual deformation of a material when it is subjected to a continuous load over time. With PTFE, this can cause a component to change shape or dimensions, potentially affecting sealing performance, clearances, alignment or the overall performance of an assembly.

This doesn't mean PTFE is unsuitable for load-bearing applications. It means that PTFE's tendency to creep needs to be considered during material selection and component design.

Fortunately, there are several ways to reduce the effects of creep, including selecting a suitable PTFE grade, using fillers, modifying the component design and, where appropriate, choosing a different engineering polymer.

Table of Contents

What is PTFE creep?

Why does PTFE creep?

PTFE creep vs cold flow

What happens if PTFE creeps?

What factors affect PTFE creep?

How can you reduce PTFE creep?

Is filled PTFE better than virgin PTFE for creep?

Can PTFE be used for load-bearing applications?

PTFE creep: the key design considerations

Does PTFE creep mean it is the wrong material?

Conclusion

What is PTFE creep?

Creep occurs when a material gradually deforms under a sustained stress.

Unlike an immediate deformation caused by applying a load, creep develops progressively. The amount of deformation depends on factors including:

  • Applied load or stress

  • Temperature

  • Duration of the load

  • Component geometry

  • PTFE grade

  • Whether the PTFE is filled or unfilled

The higher the temperature and applied stress, the more significant creep is likely to become.

For PTFE components that remain under load for long periods, creep can therefore be an important part of the design calculation.

Why does PTFE creep?

PTFE is a thermoplastic polymer with a relatively low stiffness compared with many engineering plastics and metals.

When a continuous load is applied, the polymer chains can gradually move relative to one another. Over time, this produces permanent or semi-permanent deformation.

Temperature makes this behaviour more pronounced because polymer chains have greater mobility as temperature increases.

This is why a PTFE component that performs well under a short-term load may behave differently when subjected to the same load continuously for months or years.

PTFE creep vs cold flow

The terms creep and cold flow are sometimes used interchangeably when discussing PTFE, although they can describe slightly different aspects of the material's behaviour.

Creep generally refers to deformation that develops progressively under a sustained load.

Cold flow is commonly used to describe the tendency of PTFE to deform or flow under pressure, particularly when it is compressed or mechanically loaded.

For engineering purposes, both behaviours are important because they can result in a component no longer maintaining its original dimensions.

What happens if PTFE creeps?

The consequences depend on the component and application.

Seals

In sealing applications, excessive deformation can alter the contact pressure between the seal and mating surface.

This can contribute to:

  • Leakage

  • Loss of sealing force

  • Extrusion

  • Premature failure

The risk is particularly important in high-pressure applications where the seal is subjected to significant continuous loading.

Bearings and Slide Components

A PTFE bearing or slide component can deform under continuous load.

This may alter:

  • Running clearances

  • Contact area

  • Alignment

  • Load distribution

  • Friction and wear behaviour

Precision Components

For precision-machined PTFE components, creep can result in dimensional changes that affect the fit or performance of the finished component.

This needs to be considered both during service and, in some applications, during storage or assembly.

What factors affect PTFE creep?

There isn't a single creep value that applies to every PTFE component. The behaviour depends heavily on the conditions in which the material is being used.

1. Load

Higher applied stress generally increases deformation.

A component supporting a continuous load is therefore more likely to experience significant creep than one subjected to a short-duration or intermittent load.

2. Temperature

Temperature has a significant effect on polymer behaviour.

As temperature increases, PTFE becomes more susceptible to deformation under load. An application that performs satisfactorily at room temperature may therefore require a different material or design at elevated temperatures.

3. Time

Creep is inherently time-dependent.

A component may show relatively little deformation initially but continue to change shape over an extended period.

This means that testing only short-term mechanical performance may not provide a complete picture of how a PTFE component will behave throughout its service life.

4. Component Geometry

The shape and thickness of a component can influence how stress is distributed.

Thin sections, unsupported areas and components subjected to concentrated loads may be more susceptible to deformation.

Good component design is therefore an important part of managing PTFE creep.

5. Material Grade

Not all PTFE behaves in exactly the same way.

Virgin PTFE provides excellent chemical resistance and low friction, but specific filled or modified grades can offer improved mechanical performance, including greater resistance to deformation under load.

This is where material selection becomes particularly important.

How can you reduce PTFE creep?

There are several approaches engineers can use to control creep:

Choose a filled PTFE grade

One of the most common ways to improve PTFE's resistance to deformation is to introduce a suitable filler.

Fillers can improve properties such as:

  • Compressive strength

  • Wear resistance

  • Dimensional stability

  • Resistance to deformation

  • Load-bearing capability

Common PTFE fillers include glass fibre, carbon and bronze, although the appropriate filler depends on the application.

The trade-off is that adding a filler changes the overall properties of the material. For example, a filled PTFE grade may have greater wear resistance or stiffness but may not provide exactly the same friction, chemical resistance or electrical properties as virgin PTFE.

The best filler is therefore application-dependent.

Reduce the applied stress

If the component design allows it, reducing the stress experienced by the PTFE can significantly reduce deformation.

This might involve:

  • Increasing the bearing area

  • Increasing component thickness

  • Reducing unsupported spans

  • Improving load distribution

  • Redesigning the component geometry

Sometimes a relatively small design change can make a significant difference to the amount of deformation experienced in service.

Consider operating temperature

If a PTFE component is operating close to its upper temperature limit while also carrying a continuous load, creep can become more significant.

Where possible, reducing the operating temperature can help.

However, temperature should never be considered in isolation. A material that has an acceptable temperature rating may still not have sufficient mechanical performance for a particular load and duration.

Use mechanical support

In some applications, the PTFE component can be designed so that surrounding components provide additional mechanical support.

For example, preventing a seal or bearing from deforming into an unsupported clearance can help control unwanted movement.

This is particularly important for high-pressure sealing applications, where extrusion and deformation need to be considered together.

Select a different polymer

Sometimes the best way to solve a PTFE creep problem is to use a different material.

Where high mechanical strength, stiffness and dimensional stability are more important than PTFE's exceptionally low friction, materials such as PEEK, PAI or PEI may provide a better solution.

PEEK, for example, offers substantially higher mechanical strength and stiffness than PTFE and generally has better resistance to creep under mechanical load.

However, changing material also changes other properties.

A replacement material may have:

  • Higher friction

  • Different chemical resistance

  • Different temperature limitations

  • Different wear behaviour

  • Higher material or manufacturing costs

The objective should therefore not be to find a material that simply “doesn't creep”. It is to find a material that provides the right combination of properties for the application.

Is filled PTFE better than virgin PTFE for creep?

In many applications, yes.

Filled PTFE grades are specifically developed to improve properties where virgin PTFE can be limited, including wear resistance, compressive strength and resistance to deformation.

However, “filled PTFE” is not one material.

Different fillers produce different performance characteristics, so the correct grade depends on what the component needs to achieve.

For example, a grade selected for improved wear resistance may not be the best choice where electrical properties or chemical purity are the primary concern.

Material selection should therefore consider the complete operating environment rather than simply selecting the PTFE grade with the highest filler content.

Can PTFE be used for load-bearing applications?

Yes.

PTFE is widely used in bearings, slide components, seals and other applications where it is subjected to mechanical loads.

The important consideration is whether the load, temperature, geometry, duration and required service life are compatible with the selected PTFE grade.

For higher-load applications, filled PTFE can provide improved performance compared with virgin PTFE.

For particularly demanding applications, an alternative engineering polymer may be more appropriate.

This is why PTFE should not automatically be ruled out because of its creep behaviour. Instead, its creep characteristics should form part of the engineering design process.

PTFE creep: the key design considerations

When designing a PTFE component that will remain under load, consider:

Factor Why it matters
Load Higher stress increases deformation
Temperature Higher temperatures can increase creep
Time Creep develops progressively
Geometry Unsupported or thin sections may deform more easily
Material grade Filled grades can improve resistance to deformation
Pressure Particularly important for seals and valve components
Clearance Excessive clearance can increase extrusion or deformation
Service life Long-term applications require greater consideration of creep
Mating materials Can affect friction, wear and load distribution
Manufacturing Component tolerances and machining can influence final performance

Does PTFE creep mean it is the wrong material?

Not necessarily.

PTFE's tendency to creep is a known characteristic, but it is only one part of the material-selection process.

For applications where low friction, chemical resistance and non-stick performance are critical, PTFE may still be the best choice.

Where continuous mechanical loading is the dominant requirement, a filled PTFE grade or another engineering polymer may provide better performance.

The key is to understand what the component needs to do throughout its service life, rather than selecting a material based on a single property.

Need help selecting a PTFE grade?

At Fluorocarbon, we work with engineers to select polymer materials and grades based on the operating conditions of the finished component.

That includes considering load, temperature, pressure, friction, wear, chemical exposure, dimensional requirements and manufacturing method.

Whether the solution is virgin PTFE, a filled PTFE grade or an alternative high-performance polymer, the right material should be selected around the application, not simply the material datasheet.

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