Materials #07: What Is PEEK Plastic? When to Use It in Machine Parts

In machine design, there are many times you meet parts that cannot use metal as usual.

For example:

A part in a chemical environment
A part that needs electrical insulation
A part used in a clean environment
A part that needs to be lighter than metal
A part that must not rust
A part that needs good heat resistance
A sliding part where you do not want to use oil or grease

At that point, the designer starts to think about engineering plastics.

POM, MC Nylon, PTFE, PPS, PEI, PEEK...

Among them, PEEK is a very strong material.

But also very expensive.

So PEEK is not a material you use just because you see it is good.

This article records the basic points about PEEK plastic from a machine-part design perspective: where PEEK is strong, what types exist, when to use it, and when not to.

1. What is PEEK?

PEEK stands for:

Poly Ether Ether Ketone

In Japanese it is usually called:

PEEK材 ピーク材 ポリエーテルエーテルケトン

PEEK belongs to the super engineering plastic group — in other words, a high-grade engineering plastic.

If we divide it very simply, you can picture it as follows:

Plastic material group	Examples	Quick understanding
Commodity plastics	PE, PP, PVC, ABS	Cheap, easy to use, but limited in heat resistance and not very high in mechanical properties
Engineering plastics	POM, PA, PC, PET	Used a lot in machine parts, jigs, gears, rollers
Super engineering plastics	PEEK, PPS, PEI, PI	Used in harder environments: heat, chemicals, cleanliness, high load

PEEK is in the high-grade group.

It is not the kind of plastic used for simple parts to save money.

PEEK is usually chosen when ordinary materials cannot withstand the working conditions.

In short:

PEEK is a plastic material used when you need heat resistance, chemical resistance, good retained mechanical properties, and stable operation in a hard environment.

2. Why is PEEK highly valued?

PEEK is highly valued because it balances many properties that are normally very hard to have at the same time.

Many materials are only strong in one aspect.

For example:

PTFE resists chemicals very well and has low friction, but is soft and deforms easily.

POM is easy to machine, reasonably priced, and works well for ordinary machine parts, but its heat and chemical resistance is not as good as PEEK.

Metal is hard and bears load well, but can be heavy, electrically conductive, rust, or be unsuitable in some clean environments.

PEEK is different.

PEEK has good heat resistance, good chemical resistance, good mechanical properties, good electrical insulation, and can also be machined into precise machine parts.

That is why it is used in:

Semiconductor equipment
Machines in clean rooms
Electronic inspection jigs
Chemical-resistant parts
Heat-resistant parts
Medical devices
Aerospace
Some special sliding parts

But in return, the price of PEEK is very high.

So the question when designing is not:

"Is PEEK good?"

PEEK is good. That almost needs no discussion.

The right question must be:

Does this part really need to use PEEK?

3. The main properties of PEEK

When choosing PEEK, look by each group of properties.

Do not just hear "PEEK is really premium" and put it on the drawing.

Good heat resistance

PEEK has very good heat resistance compared to many other engineering plastics.

In many documents, the continuous service temperature of PEEK is usually around 240 to 260°C, depending on the grade and working conditions.

This is a very high level for a thermoplastic.

For many machine parts, if POM, PA, PC do not have enough heat resistance, PEEK can be an option to consider.

However, heat resistance does not mean you can just put it in a hot environment and be done.

You still need to check:

Continuous temperature or short-term temperature?
Is there a mechanical load while it is hot?
Are there chemicals at the same time?
Is there a precision dimension requirement after heating?
Does it creep under long-term load?

Material design should not just look at one temperature number.

Good chemical resistance

PEEK resists many kinds of chemicals very well.

This is why PEEK is often used in chemical-processing equipment, semiconductor equipment, and jigs in special environments.

But no material is immortal against every chemical.

PEEK still has environments that need careful checking, for example some special strong acids.

So if using it in a chemical environment, you need to ask clearly:

What is the chemical?
What concentration?
What temperature?
How long is the contact time?
Is it continuously immersed or just splashed on?
Is there a mechanical load during chemical contact?

Just writing a generic "chemical resistant" is not enough.

Better mechanical properties than many ordinary plastics

PEEK has good mechanical strength and hardness compared to many engineering plastics.

It can be used for parts that need to keep a more stable shape, bear load better, or work at temperatures where other plastics start to weaken.

Still, PEEK is a plastic.

You should not compare it directly with steel and expect it to bear load like steel.

When using PEEK for a load-bearing part, you still have to check:

Stress
Deformation
Creep over time
Working temperature
Load direction
Wall thickness
Sharp corners causing stress concentration
Assembly conditions

In particular, for parts that are bolt-tightened, press-fitted, or clamped long-term, pay attention to creep.

Plastic can deform gradually over time under load.

PEEK resists creep better than many other plastics, but that does not mean it does not creep.

4. PEEK is not just one type

This is a very important point.

Many people say "use PEEK" as if PEEK is only one type.

In reality, PEEK has many different grades.

Each grade is created for a different purpose.

Some prioritize strength and toughness.

Some prioritize hardness.

Some prioritize sliding.

Some prioritize anti-static.

Some are for medical use.

Some are for semiconductors.

So writing on the drawing like:

Material: PEEK

is often not enough.

If the part is important, you should note the grade clearly or at least the required performance.

For example:

PEEK natural
PEEK GF30
PEEK CF30
PEEK sliding grade
PEEK ESD / conductive grade
PEEK medical grade

Choosing the wrong grade is still PEEK, but the result can be very different.

5. PEEK natural – the basic type, the first one that comes to mind

PEEK natural is the unreinforced type, usually light brown or a natural color depending on the manufacturer.

This is the basic PEEK.

The advantage of PEEK natural is a good balance between:

Strength
Toughness
Heat resistance
Chemical resistance
Electrical insulation
Machinability

If there is no special requirement such as sliding, anti-static, increased hardness or medical, PEEK natural is usually the starting point to consider.

But you should not default to natural for every case.

If the part needs higher hardness, PEEK natural may not be enough.

If the part is a dry sliding bush, PEEK natural is not necessarily a good choice either.

If the part is used in an ESD environment, PEEK natural can accumulate charge.

So natural is the easy type to start with, but not the type that solves every problem.

6. PEEK GF – increased hardness with glass fiber

PEEK GF is usually PEEK reinforced with glass fiber.

A common example is the type with about 30% glass fiber.

The main purpose is to increase:

Hardness
Dimensional stability
Load capacity
Resistance to deformation at high temperature

This type is more suitable when the part needs to keep its shape well, warp less, or bear a higher load than PEEK natural.

But there is a point to note.

When glass fiber is added, the material is usually harder but the toughness can drop.

To put it more plainly:

Harder does not mean less prone to failure in every case.

The part can resist deformation better, but it can also chip or crack more easily if the design has sharp corners, impact, or an unreasonable press-fit.

Also, PEEK GF is harder to machine than PEEK natural.

Glass fiber wears the tool faster.

If the machining shop is not familiar with it, the surface can turn out poor, the dimensions unstable, or the part edges easily chipped.

7. PEEK CF – increased hardness with carbon fiber

PEEK CF is PEEK reinforced with carbon fiber.

Compared to PEEK GF, this type usually has higher hardness, better dimensional stability, and better performance in some applications needing wear resistance or better thermal conduction.

PEEK CF is usually considered for:

Parts requiring high hardness
Parts needing dimensional stability
Parts working at high temperature
Some sliding or wear-bearing parts
Mechanisms needing weight reduction compared to metal

But this type also has drawbacks.

Higher price.

Harder to machine.

The tool wears faster.

The material can also be more brittle than the natural type.

If the part has small grooves, sharp corners, small holes, small threads or thin walls, you need to check machinability carefully.

Do not see CF as "more premium" and choose it right away.

In many cases PEEK natural or PEEK GF is already enough.

Choose CF when you truly need the properties of CF.

8. PEEK sliding grade – not every PEEK slides well

This is a place very easily misunderstood.

Many people hear PEEK is a premium plastic and think PEEK slides well.

Not necessarily.

PEEK natural is not always suitable for a dry sliding part.

If you need to make a sliding bush, a slider, or a friction part, you need to look at the sliding grade.

PEEK sliding grade is usually blended with additives such as:

PTFE
Graphite
Carbon fiber
Other solid lubricants

The purpose is to reduce friction and increase wear resistance.

This type is more suitable for positions that:

Do not want to use oil or grease
Must not generate much dirt
Need to run in a clean environment
Need stable friction
Need better heat resistance than ordinary POM or PTFE

But for a sliding part, you cannot just choose the material and be done.

You need to check further:

Surface load
Sliding speed
Heat generated
The mating material
The surface roughness of the mating part
Whether there is dust, chemicals or water
Whether it runs fully dry or with light lubrication

In sliding-part design, the material is only one part.

The mating surface and the real running conditions matter just as much.

9. PEEK ESD / conductive – used when static electricity must be controlled

PEEK natural usually has good electrical insulation.

This is beneficial in many cases.

But in a semiconductor, electronics, clean room or sensitive-component-handling environment, insulation that is too good can cause a problem.

The material can accumulate charge.

When an electrostatic discharge occurs, electronic components can be damaged.

That is why there are anti-static or conductive PEEK grades.

These types are usually blended with carbon or a conductive filler to adjust the surface resistance.

The goal is not always to be strongly conductive.

In many cases you just need the charge to drain gradually, avoiding charge buildup and avoiding a sudden discharge.

PEEK ESD is usually used for:

Jigs that pick electronic components
Component support trays
Parts in semiconductor equipment
Fixtures in clean rooms
Parts contacting near ESD-sensitive products

If the environment has an ESD requirement, you should not use PEEK natural by feeling.

You need to choose the right grade and check the resistance parameters per the customer's requirement or internal standard.

10. Where is PEEK used a lot?

PEEK usually appears in places where ordinary materials do not meet the requirements enough.

Semiconductor equipment and clean rooms

This is one of the fields that often use PEEK.

The reason is that PEEK has many suitable properties:

Good chemical resistance
Good heat resistance
Less particle generation than some other materials if used correctly
Has anti-static grades
Can be precisely machined
Suitable for many parts in a clean environment

For example:

Locating jigs
Support trays
Clamping parts
Guides
Spacers
Insulators
Parts in areas with chemicals or heat

However, the clean room environment does not only ask what the material is.

You also have to look at:

Does it generate particles?
Does it outgas?
Does it contact any chemicals?
Is there an ESD requirement?
Is a colored material or filler allowed?
Is a material certificate required?

PEEK is a strong candidate, but you still have to check against the specific requirements.

Medical devices

PEEK is also used in the medical field because it can withstand sterilization, is stable, and has some biocompatible grades.

But this is a special area.

If used for medical purposes, you cannot take ordinary industrial PEEK and use it carelessly.

You need the right medical grade, the right certification, the right material control and the right production process.

For ordinary machine design, you should only understand that PEEK has medical applications, but not infer that any PEEK can be used for medical purposes.

Insulating, heat-resistant parts

PEEK has good electrical insulation and high heat resistance, so it can be used for:

Insulators
Spacers
Holders
Parts near a heat source
Parts in an electrical assembly needing better mechanical strength than ordinary plastic

But if the goal is only simple insulation at normal temperature, PEEK can be too expensive.

In that case you can consider other materials first, for example POM, MC Nylon, PPS, PEI, epoxy glass, ceramic... depending on the conditions.

Special sliding parts

With a suitable grade, PEEK can be used for sliding parts in a hard environment.

For example:

Cannot be lubricated
High temperature
Has chemicals
Needs cleanliness
Needs weight reduction
Needs to avoid metal

But you should not see "sliding" and choose PEEK right away.

POM, PTFE, UHMW-PE, bronze, standard bearings, linear guides... can be more suitable depending on the case.

PEEK is only worth using when the working conditions truly require it.

11. The biggest drawback: high price

PEEK is expensive.

This must be said clearly.

In many cases, the material price of PEEK can be much higher than POM, PA, PTFE or ordinary engineering plastics.

Not to mention if you choose a special grade such as CF, sliding, ESD, medical grade, the price is even higher.

Besides the material cost, there is machining cost.

PEEK is not always easy to machine.

If the part needs high precision, it may need:

Better tooling
More suitable cutting conditions
Better heat control
Separate roughing and finishing
Stress-relief annealing
Dimensional inspection after machining
Control of distortion after unclamping

So when choosing PEEK, do not just compare price by material per kg.

You need to look at the whole picture:

If this part fails, how much is the loss?
Does a machine stop cost more than the material money?
Does it reduce maintenance?
Does it reduce contamination risk?
Does it increase service life?
Does it avoid using metal or oil/grease?
Is there a mandatory customer requirement?

If PEEK helps the machine run more stably, reduces defects, reduces downtime, reduces contamination, then the high price can be reasonable.

But if it is just a simple spacer at normal temperature, no chemicals, no special requirement, then using PEEK can be a waste.

12. Machining PEEK needs care

PEEK can be machined.

It can be made from:

Sheet
Round bar
Tube
Cast or extruded stock depending on the supplier

But machining PEEK is not like machining metal, nor exactly like POM or MC Nylon.

Some points to note:

Prone to generating heat when cutting

PEEK is a plastic, so the heat during machining needs to be controlled.

If the cutting conditions are unsuitable, the material can overheat, have many burrs, a poor surface or unstable dimensions.

Reinforced types wear the tool

For PEEK GF or PEEK CF, the internal filler can wear the tool fast.

If the tool wears, the surface degrades, the dimensions drift, and the edges chip or burn.

So for reinforced PEEK parts, you should discuss with the machining shop in advance.

Do not just send the drawing as if it were an ordinary plastic part.

Can warp after machining

PEEK is a semi-crystalline material.

The stock can have residual stress from the production process.

When machining removes material, the internal stress is released, and the part can bend, warp or change dimensions.

This is more likely to happen with:

Thin parts
Long parts
Parts where material is removed unevenly on both sides
Parts requiring high flatness
Parts requiring tight tolerances

In those cases, you may need to rough machine, stress-relief anneal, then finish machine.

In Japanese this is usually called:

アニーリング処理

In English it can be called:

stress-relief annealing or annealing

This is a point to ask the supplier or machining shop before finalizing the drawing.

13. When should you use PEEK?

You can consider PEEK when the part has one or more of the following conditions:

High working temperature
Has chemicals
Needs insulation but still needs good mechanical properties
Needs a clean material for a clean room
Needs anti-static via a special grade
Needs a part lighter than metal
Needs wear resistance or sliding in a hard environment
Needs better dimensional stability than ordinary plastic
A cheaper material was tried but did not meet the requirement
The customer or standard specifies PEEK

A practical example:

A small guide part in an ordinary machine, normal temperature, no chemicals, no ESD, no large load.

In this case choosing PEEK can be overkill.

But a clamping part in semiconductor equipment, near chemicals, needing cleanliness, needing heat resistance and not wanting to use metal.

In this case PEEK is worth considering.

Good design is not always choosing the premium material.

Good design is choosing a material just sufficient for the working conditions.

14. When should you not use PEEK?

You should not use PEEK just because you heard it is good.

Some cases to reconsider:

You only need an easy-to-machine, reasonably priced plastic

If the part is just a simple support, cover, or spacer at normal temperature, POM or MC Nylon can be enough.

You only need chemical resistance but no high load

PTFE or another fluororesin can be more suitable, depending on the chemical.

You only need light sliding under normal conditions

POM, UHMW-PE, MC Nylon, PTFE or a standard bush can be more economical.

The part is too large

PEEK is very expensive.

The larger the part, the more painful the material cost.

Before choosing PEEK for a large part, you should re-check whether you can:

Use PEEK only at the important contact area
Use a small PEEK insert
Use metal for the main body
Use another cheaper material
Change the structure to reduce the amount of PEEK

The drawing does not state the requirement clearly

If the drawing only writes "PEEK" without a clear reason for the choice, without a clear grade, without a clear working environment, it is very easy to choose wrong.

For an expensive material like PEEK, all the more you need to note the requirement clearly.

15. How to note PEEK on the drawing to reduce ambiguity?

For a simple part, many companies may only write:

Material: PEEK

But for an important part, you should be clearer.

For example:

Material: PEEK natural

or:

Material: PEEK GF30

or:

Material: PEEK sliding grade

or:

Material: PEEK ESD grade

If there is a specific material manufacturer, you can note by material code or an equivalent grade.

For example:

Material: PEEK natural, Ketron 1000 PEEK or equivalent

or:

Material: PEEK CF30 or equivalent

Depending on the company and customer, the way of noting can differ.

But the principle is:

Do not let the buyer or the machining shop have to guess the PEEK type.

If you need anti-static performance, you must note the resistance requirement.

If you need a sliding grade, you must note clearly that it is a sliding grade.

If you need a medical grade, you must note the grade and the required certification clearly.

If you need color, cleanliness, or a material certificate, you should also note it from the start.

16. Checklist when choosing PEEK for a machine part

Before finalizing PEEK, do a quick check:

Working conditions

What is the working temperature?
Continuous or short-term temperature?
Are there chemicals?
Is there steam, hot water, solvent, oil, grease?
Is there a clean room requirement?
Is there an ESD requirement?

Load and mechanical properties

What load does the part bear?
Static or dynamic load?
Is there impact?
Is it bolt-tightened, press-fitted, clamped long-term?
Is there a creep risk?
Is high hardness required?

Material grade

Is PEEK natural enough?
Is GF or CF needed?
Is a sliding grade needed?
Is an ESD / conductive grade needed?
Is a medical grade needed?
Is a material certificate needed?

Machining

Is the part thin, long, prone to warping?
Is the tolerance too tight?
Is stress-relief annealing needed?
Does the machining shop have PEEK experience?
Have the tooling, surface, burrs and sharp edges been considered?

Cost

Is there a cheaper material that is still sufficient?
Can PEEK be used only at the important part?
What is the consequence if this part fails?
Does using PEEK reduce downtime, defects, maintenance?
Is the high price accepted by the customer?

Going through this checklist will avoid choosing a material by feeling.

Conclusion

PEEK is a very strong material.

Good heat resistance. Good chemical resistance. Good mechanical properties. Good electrical insulation. Many grades for many hard environments.

But PEEK is also very expensive and not always easy to machine.

For an ordinary machine part, you should not choose PEEK just to "be safe".

If POM, MC Nylon, PTFE, PPS or another material is already enough, then using PEEK can be a waste.

Conversely, if the part is in a high-temperature, chemical, clean room, or ESD environment, or needs a stability that ordinary materials cannot provide, PEEK is a very worthwhile choice to consider.

The most important point is not to write "PEEK" ambiguously.

You need to know whether you need PEEK natural, PEEK GF, PEEK CF, a sliding grade, an ESD grade or another special grade.

Material design is not choosing the best material.

Material design is choosing the right material for the right working conditions, at a reasonable cost and with the lowest risk.

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