Overview
PEEK (polyetheretherketone) is the workhorse high-performance thermoplastic for environments where engineering plastics fall short and metal is either too heavy, too conductive, or chemically incompatible. It maintains usable mechanical properties to ~250°C continuous service, resists nearly every common chemical at elevated temperature, and is inherently flame retardant without additives. The cost premium — typically 30–80× that of engineering plastics like PA66-GF — limits PEEK to applications where the failure of a cheaper material would itself be expensive.
Three things drive PEEK selection: continuous service above 150°C, chemical exposure that destroys lower-tier resins, and implant-grade biocompatibility. Outside those drivers, glass-filled PA66, PBT, or PPS will usually deliver adequate performance at a fraction of the cost.
Machining notes
PEEK machines well with the right tooling. Use sharp carbide inserts with positive rake, run at 300–500 SFM, and flood coolant continuously. Chips form long and ribbon-like at moderate feeds — high feed rates produce stringy chips that wrap on the tool; very low feeds glaze the cut surface and accelerate tool wear from rubbing. Aim for 0.002–0.008 in/rev on turning and proportional feed-per-tooth on milling.
Glass- or carbon-filled PEEK is highly abrasive. Carbide will work for prototype quantities; for production runs, polycrystalline diamond (PCD) tooling pays for itself within the first job. Expect tool life on filled PEEK to be 5–10% of that on unfilled.
Surface finish of 32 Ra is straightforward; 16 Ra is achievable with sharp finishing passes and shallow depth of cut. Annealing is not required for unfilled stock — the rod and plate stock from major suppliers is already stress-relieved. After heavy machining (large material removal), a stress-relief anneal at 150°C for 2 hours per inch of section thickness reduces post-machining dimensional drift.
Bonding is the weak point. PEEK’s surface energy is too low for most adhesives without preparation. Plasma treatment, chromic acid etch, or flame treatment activates the surface; epoxies and cyanoacrylates work after activation. Mechanical fasteners and ultrasonic or laser welding are the standard joining methods in practice.
Variant guidance — when to pick which grade
- Unfilled (450G / Ketron LSG) — the default. Pick this unless you specifically need the properties below. Best machinability, retains FDA compliance, best toughness.
- GF30 — pick when stiffness and dimensional stability under load matter more than impact resistance. Structural brackets, housings under thermal cycling.
- CF30 — pick when stiffness-to-weight is paramount or when EMI shielding is required. Semiconductor handling, aerospace structural. Plan on PCD tooling.
- Bearing grade (HPV / PVX) — pick for self-lubricating bearings, bushings, seals running dry or under marginal lubrication. Not for food contact.
- Medical grade (LSG / OPTIMA) — only when USP Class VI or ISO 10993 certification is required. Cost is roughly 2–3× standard unfilled. Use Ketron CLASSIX LSG or Victrex PEEK-OPTIMA depending on supplier relationship.
Process caveats
FDM is possible but requires industrial equipment. Most printers marketed for “high-performance polymers” cannot reliably print PEEK — per AON3D’s published analysis, the majority fall short of the chamber and hotend temperatures the material actually requires. Real requirements:
- Nozzle: 400–440°C, all-metal hotend
- Heated chamber: 120–150°C minimum, ideally approaching Tg (143°C)
- Bed: 160°C+
- Filament drying: 120–150°C for 4+ hours immediately before printing
- Post-print annealing: 200–300°C for 1–2 hours to develop crystallinity
Without all of those, FDM PEEK parts delaminate, warp, or fail to develop the crystalline microstructure that gives PEEK its mechanical properties. Annealed printed parts can approach 80% of injection-molded strength; unannealed parts top out around 50–60%.
Injection molding is straightforward on equipment rated for high-temp resins (typically 400°C+ barrel capability). Tooling steel must be capable of running at 200°C continuously. Drying is non-negotiable — undried PEEK produces bubbles and brittle parts.
Thermoforming is possible but the processing window is narrow because of PEEK’s sharp melting point and semi-crystalline behavior. Sheet sag is hard to control without specialized equipment.
Failure modes worth designing around
The chemical resistance reputation is mostly earned, with two real exceptions: concentrated sulfuric acid above ~80°C will degrade PEEK over time, and concentrated nitric acid attacks it. Below 80°C the sulfuric resistance is excellent. Both are documented in Victrex and Solvay datasheets.
UV degradation is the second real exposure. Unstabilized PEEK in continuous outdoor service yellows within months and embrittles within a year or two. For outdoor structural use, pick a carbon-filled grade (the carbon both stabilizes and pigments) or a UV-stabilized compound.
PEEK is notch-sensitive at elevated temperature. Below 100°C it tolerates sharp corners reasonably. Above 200°C under cyclic loading, sharp notches become crack initiation sites — generously radius any stress concentrations in parts that will see thermal cycling.
Applications by industry
- Aerospace: brackets, bushings, fuel-system seals, electrical connectors, thermal isolators. NASA and major airframers have qualified PEEK for non-load-critical interior and engine-bay applications.
- Medical: spinal cages (interbody fusion devices) are the highest-volume implant application; dental abutments, surgical instrument components, trial implants.
- Oil and gas: downhole tool seals, back-up rings, electrical isolators in directional drilling tools. PEEK and PEK are standard above 200°C bottomhole temperatures.
- Semiconductor: wafer carriers, vacuum-chamber components, plasma-etch fixturing. CF30 grade is preferred for ESD-controlled environments.
- Chemical processing: pump impellers, seal faces, valve components, thermowell housings in aggressive chemistries.
- Food and pharma: only with FDA grades — generally unfilled or specifically compounded medical/food grades.