What Is the Melting Point of PEEK and Why Does It Matter?

PEEK CNC milling with thermal property context for high-performance polymer

Quick answer

Virgin PEEK typically melts around 343°C (649°F). That high melting point enables high continuous-use temperatures—but on a CNC it mainly reminds you that PEEK stores heat in the cut. Protect crystallinity and tolerance with sharp tools, real chip load, and controlled fixturing—not by “babying” the spindle into rubbing.

PEEK’s melting point is one reason it shows up in aerospace, medical, and semiconductor hardware. Understanding Tm alongside glass transition and HDT helps you machine it without burning the surface or losing flatness.

Understanding PEEK’s Melting Point

PEEK is semi-crystalline. The melting point near 343°C reflects crystal breakdown during processing. Glass transition for many grades sits much lower (often cited around ~143°C), which influences stiffness as temperature rises even while the material remains far from melt.

Compare with other high-temp options in PEEK vs PTFE and the broader CNC plastic melting point chart.

Why Tm Matters in Processing and CNC

Context	Why 343°C matters
Injection / extrusion	Sets processing window and thermal history
Service temperature	Supports high continuous-use ratings vs many plastics
CNC milling / turning	Signals high thermal demand; edge heat still risks surface damage
Filled grades	Fillers raise abrasion and can change heat flow in the cut

Machining implications

Prefer carbide tooling with sharp edges; avoid polished rubbing
Take chips—not dust—especially on finish passes
Use air blast or appropriate coolant strategy for the grade and shop standard
Allow for heat-driven expansion when probing tight tolerances mid-cycle

Shop tip: If the surface looks glazed, you likely overheated the skin. Reduce rub, restore chip thickness, and re-check tool wear before blaming “PEEK is hard to hold.”

Melting Point vs Service Temperature

Do not treat Tm as the continuous-use limit. Designers rely on mechanical property retention, HDT, and application standards. Tm explains why PEEK can be processed and used far above acetals like those in POM vs nylon comparisons—it does not license running a part at 340°C under load.

Fillers and Thermal Behavior

Glass- and carbon-filled PEEK grades shift stiffness, wear, and machinability. Melting point of the polymer matrix remains in the same neighborhood, but abrasive fillers increase tool wear and can change how heat leaves the cut. Always machine to the cert on the blank.

Practical Applications Driven by Thermal Performance

High-temp fixtures and seal carriers
Semiconductor and vacuum-compatible components (grade-dependent)
Medical instruments and devices where sterilisation and strength matter (regulatory grade dependent)
Aerospace brackets and insulating structural parts

Comparing PEEK to Nearby High-Temp Plastics

Against PPS, PEEK typically offers higher toughness and a different chemical profile at similar “high temp” marketing language—always compare datasheets at your temperature. Against PTFE, PEEK wins structure; PTFE wins inertness and slip. Against acetals, PEEK’s melting point and service window are in another league, which is why PEEK blanks cost more and deserve more process discipline.

Inspection after heat

For tight PEEK jobs, measure after the part returns to room temperature. In-process probes on a hot surface can lie by enough to fail a press-fit later. Build a cool-down step into the traveler when tolerances are below ~0.05 mm on critical fits.

Frequently Asked Questions

Is PEEK’s melting point always 343°C?

That is the widely cited value for many virgin grades. Confirm the supplier datasheet—especially for blends and highly filled compounds.

Does a higher melting point make CNC easier?

Not necessarily. PEEK still demands heat discipline and sharp tooling. Higher Tm mainly expands the thermal design space versus commodity plastics.

How does PTFE compare thermally?

PTFE also has a high melting region (~327°C) but lacks PEEK’s structural strength—see PEEK vs PTFE selection guide.

Conclusion

PEEK’s ~343°C melting point is a cornerstone of its high-temperature reputation. For CNC teams, it is a cue to respect heat at the tool edge, preserve surface integrity, and probe tolerances with thermal soak in mind. Share grade, filler, and tolerance stack with your machinist to keep expensive blanks out of the scrap bin.