PEEK vs PEKK: Which High-Performance Material Should You Choose?

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  PEEK vs PEKK at a glance
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  Why PEEK vs PEKK starts from the same family
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  Stiffness, impact and wear: where PEEK vs PEKK diverges
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  Chemical resistance and high-temperature limits
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  Machining and processing differences that reach the shop floor
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  Cost and availability: the quiet tiebreaker
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  How to run the PEEK vs PEKK decision on your own part

PEEK and PEKK both belong to the polyetherketone family. Their chains are built from aromatic rings linked by ether and ketone groups. That rigid backbone is why both hold shape above 250 °C, resist most solvents, and burn with low smoke. Neither one is a commodity plastic with a fancy name.

The practical overlap is wide. Both take continuous service near 250 °C, both are electrically insulating, and both can be machined, injection molded or 3D printed. If your part only needs heat resistance and general chemical resistance, either resin will usually pass the test.

The split appears when you push one property hard. PEEK has a higher ketone fraction, which packs the chain tightly and speeds up crystallization. PEKK carries more ether linkages, which lowers the melting point and slows crystallization. Those two structural facts drive almost every difference later in this article.

So the question is rarely which material is better. It is which failure mode matters most in your application.

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  Same familyBoth are polyetherketones with aromatic backbones.
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  Same ceilingBoth handle roughly 250 °C continuous service.
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  Different balanceKetone content drives stiffness and wear; ether content drives toughness.

Unfilled PEEK sits near 3.6–4.0 GPa tensile modulus. Unfilled PEKK runs a little higher, often 4.0–4.5 GPa, so thin walls and slender ribs hold their shape better. If your design is stiffness-limited and you cannot add material, PEKK gives you a small but real margin.

Impact is the other direction. PEKK absorbs more energy before cracking because its slower crystallization leaves a tougher microstructure. Parts with sharp corners, press fits or shock loads tend to survive longer in PEKK. PEEK can crack at a corner that PEKK would tolerate.

Wear favors PEEK in unfilled grades. Its higher crystallinity gives a harder surface, and it holds a polished finish well. For bushings, thrust washers and sliding pads running dry against steel, unfilled PEEK is usually the starting point.

Fillers change the ranking. Carbon-fiber PEKK closes much of the wear gap and adds stiffness, but it also becomes abrasive and harder to machine. Choose fillers only when the unfilled grade has already failed a test.

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  StiffnessPEKK is typically 10–15% stiffer unfilled.
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  ToughnessPEKK takes more impact before cracking.
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  Dry sliding wearUnfilled PEEK wins against steel counterfaces.

PEEK resists a longer list of aggressive chemicals. Strong solvents, steam, hydraulic fluids and most acids leave it alone at room temperature and often at elevated temperature too. PEKK handles the common industrial chemicals well but sits slightly behind on the harshest solvent exposures.

If your part sees repeated steam autoclave cycles, PEEK is the safer pick. Medical and food-processing hardware often specifies it for exactly this reason. PEKK still works in many sterilization routes, but the margin is thinner.

Temperature is closer than most people expect. PEEK melts near 343 °C and PEKK near 338 °C, so the melting gap is only a few degrees. The useful difference is the glass transition: PEKK sits near 165 °C against roughly 143 °C for PEEK. That higher Tg means PEKK keeps more of its stiffness as the part heats up.

For a bracket that must stay rigid at 150–170 °C, PEKK often outperforms PEEK even though its melting point is lower.

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  Harsh solventsPEEK has the wider resistance envelope.
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  Steam and autoclavePEEK is the conservative choice.
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  Hot stiffnessPEKK holds modulus better above 140 °C.

PEEK machines like a hard, brittle plastic. Sharp tooling, high spindle speed and light chipload keep the cut clean. It chips rather than smears, so you can hold tight tolerances and a good surface finish without special tricks. Deburring is straightforward.

PEKK behaves more like a tough, gummy resin. It wants lower feed per tooth and a slightly larger edge radius, otherwise the material pushes away from the cutter and you fight chatter. Tool wear runs higher, and deep pockets need more patience.

Crystallization speed matters if you are molding rather than cutting. PEEK crystallizes quickly, which suits fast cycle times. PEKK cools slowly, which helps thick sections avoid internal voids and residual stress but extends cycle time.

For prototypes and low-volume runs, both machine on the same 3-axis and 5-axis equipment. The cutting parameters differ, not the setup. On our 16 simultaneous 5-axis centers, PEKK parts usually need a smaller stepover and a slower finishing pass.

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  PEEKHard and chippy; easy to finish and inspect.
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  PEKKTough and gummy; slower feeds, more tool wear.
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  MoldingPEEK cycles fast; PEKK fills thick sections better.

PEEK has decades of supply behind it. Stock shapes come in more diameters and grades, and pricing is more predictable. That availability matters when you need a replacement part next week.

PEKK is produced by fewer suppliers, so lead times and prices move more. It can cost noticeably more per kilogram, and specialty grades may carry a minimum order. For a one-off prototype, that gap is easy to absorb. For a 10,000-part run, it is not.

Compare the total part, not the resin price. If PEKK lets you delete a stiffening rib or drop a wall thickness, the material premium may vanish in the machining and assembly steps. If PEEK avoids a coating or a liner, the same logic applies in reverse.

Ask for both quotes before committing. A material decision that ignores the machining cost is only half a decision.

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  Stock shapesPEEK is available in more sizes and grades.
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  Price stabilityPEEK is more predictable year to year.
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  Design savingsPEKK stiffness can remove material elsewhere.

Start with the failure mode you are trying to avoid. If the answer is wear, chemical attack or steam exposure, lean toward PEEK. If the answer is cracking at a corner, deflection under load, or stiffness at 150 °C, lean toward PEKK.

Next, check the temperature profile against the glass transition, not the melting point. A part that only sees 120 °C will behave similarly in both resins. A part that sees 160 °C will not.

Then look at the geometry. Thin walls, long unsupported spans and press fits reward PEKK. Thick sections with tight tolerances and a polished sliding surface reward PEEK. Sharp internal corners are a warning sign for PEEK.

Finally, run one test. Machine both grades to the same drawing and put them through the real load, the real chemical and the real temperature. Two samples will settle in a week what a datasheet debate cannot settle in a month.

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  Wear or chemicalsChoose PEEK.
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  Cracking or stiffnessChoose PEKK.
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  Above 140 °CCheck Tg before you decide.