PEEK Plastic Grades for Machining: Selection Guide

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Quick Specs: PEEK Plastic for CNC Machining

Chemical Name	Polyetheretherketone (PEEK)
Polymer Family	Polyaryletherketone (PAEK) — semi-crystalline thermoplastic
Continuous Service Temperature	250°C (482°F)
Melting Point	343°C (649°F)
Tensile Strength (Unfilled)	90–100 MPa (13,000–14,500 psi)
Elastic Modulus	3–4 GPa
Common Machined Forms	Rod, sheet, tube, injection molded blanks
Key Grades for Machining	Unfilled (450G), GF30, CF30, Bearing, Medical (PEEK-OPTIMA)
Achievable CNC Tolerance	±0.025 mm (±0.001 in) standard; ±0.02 mm with annealing

Selecting the wrong PEEK grade for a CNC project can multiply costs tenfold — or yield parts that fail under service conditions. PEEK (polyetheretherketone) is a high-performance thermoplastic offering strong mechanical properties, chemical resistance, and heat tolerance. But the material comes in at least six distinct grades, each with different machining behavior, cost structure, and regulatory standing.

This guide briefly compares unfilled, glass-filled, carbon fiber reinforced, bearing-grade, and medical-grade peek on a side by side basis – including real property data, machining parameters, tool wear rates, and a grade selection matrix that maps the differentials in each variant against the specific application requirements. No matter whether you require precision PEEK CNC machining for aerospace bushings or semiconductor fixturing, or critical surgical implants, the right grade decision path starts here.

What Is PEEK — and Why Does Grade Selection Matter for Machining?

peek is a semi-crystalline, thermoplastic polymer made from repeating ether-ether-ketone units optimized for stiffness, strength and chemical stability. Developed by Imperial Chemical Industries in the early 1980s, A 2024 review published in the National Institutes of Health database shows an elastic modulus of 3-4 GPa, a strength averaging 80-97 MPa, and a Tg of 143C — figures that place it well above most engineering plastics like nylon, acetal and polycarbonate.

What makes PEEK plastic properties unusual among thermoplastics is the combined heat resistance (steady service at 250°C), broad chemical resistance (survives hydrocarbons, ketones, and dilute acids), and dimensional stability under sustained mechanical loads. These properties make it a common metal replacement in harsh environments — but choosing the wrong grade leads to problems from excessive cost to outright part failure.

Specifically for machining, grade choice is an important factor as each PEEK variant has its own machining profile. Unfilled PEEK machines smoothly with standard carbide tooling. Mix in 30% glass fiber to the mix and the tool life is 50-70% shorter. Add carbon fiber reinforcement and the conductivity changes, affecting flow, chip formation and dimensional control. Medical grades impose special regulatory considerations and constraints, affecting everything from raw material to shop floor cleanliness.

💡 Key Takeaway

Your PEEK grade choice affects not just part properties, but tooling strategy, machining costs, and compliance pathway. $40 a kilo industrial-grade and $500 kilo medical-grade rods may appear to be identical – but getting this wrong is an expensive mistake.

PEEK Grade Categories — Unfilled, Reinforced, and Specialty Variants

peek material grades can broadly be split into three families: unfilled (neat), fiber-reinforced and specialties. Below, a comparison matrix puts specific numbers where the theory belongs – because we need actual values to make informed material choices, not just generic descriptions.

Grade	Filler	Tensile Strength	Max Service Temp	Typical Application	Raw Cost (USD/kg)
Unfilled (450G)	None	90–100 MPa	250°C	Seals, insulators, general structural	$40–90
GF30	30% glass fiber	130–160 MPa	250°C	Pump housings, semiconductor fixtures	$60–120
CF30	30% carbon fiber	140–210 MPa	250°C	Aerospace brackets, high-precision shafts	$80–150
Bearing Grade	PTFE + carbon + graphite	70–90 MPa	250°C	Bushings, thrust washers, sliding seals	$70–130
Medical (PEEK-OPTIMA)	None (ultra-pure)	100 MPa	250°C	Spinal cages, dental abutments, implants	$500–800
ESD/Conductive	Carbon black or carbon fiber	85–100 MPa	250°C	Wafer handling, electronics test sockets	$90–160

From the cost perspective, the key to understanding most PEEK machining guides is that medical-grade peek-OPTIMA costs 6-10x more than industrial-grade unfilled PEEK. According to the NIH-published biomedical materials review, the typical price of raw medical grade PEEK (any brand) is 500-800 /kg, and that dictates the costs to the end project, machining and all.

Each grade of PEEK plastic is characterized according to ASTM standards– ASTM D6262 covers general peek classification for molding and extrusion grade materials, whereas ASTM F2026 governs peek polymers for intended surgical implant use. Understanding which specification relates to your process specifies everything from traceability of custom PEEK machined parts to incoming material inspection procedures.

Unfilled PEEK (450G / Ketron 1000) — The Baseline Machining Grade

Unfilled peek is most often the starting point for most plastic machining projects that do not demand fiber reinforcement or regulatory compliance. Granular extruded rod, sheet, and tube offerings- equivalents to 450G- grades- provide tensile strengths at 90-100 MPa with an elongation at break near 30%, and having crystallinity characterized in the 30-40% range as validated through peer-reviewed material analytical studies marketed through the U.S. National Institutes of Health.

Machining unfilled peek with typical carbide tooling is well-understood relative to reinforced PEEK grades- tooling life remains predictable and the material produces chips cleanly without the heavy load associated with carbon fibers or glass reinforced material. Typical CNC turning speeds are in the range of 300-800 surface feet per minute (SFM), with face milling at 500-800 SFM and end milling at 270-450 SFM.

✔ Advantages

Highest toughness and elongation among PEEK grades
Best fatigue resistance for cyclic loading applications
Lowest material cost ($40–90/kg)
Longest tool life during CNC machining
FDA-compliant grades available for food contact

⚠ Limitations

Lower stiffness than CF30 reinforced grades (flexural modulus 4 Gpa versus 10+ Gpa for CF30 reinforced)
Higher thermal expansion coefficient- tighter tolerance work may necessitate annealing
Not suitable for high-wear sliding contact without PTFE modification
Creep under sustained loads at elevated temperatures

📐 Engineering Note

For unfilled peek portions requiring tolerances tighter than 0.05 mm, stress-relief annealing should occur prior to precise final machining. Slowly increase temperature of oven to 200-220 Celsius, maintain for 1-2 hours (roughly 30 minutes per 10 mm of stock being processed), then allow oven to cool gradually. This heats to relieve residual stresses from extrusion or rough machining which would lead to dimensional movement after final cuts.

⚠️ Common Mistake

Many industry engineers discourage the use of flood coolant while machining peek as thermal shock- the rapid rate of temperature change caused by coolant application- can induce micro-cracking of the material. It is safer to use air jets or light water-soluble coolant mists. If cooling is invoked, do not bring the coolant stream into contact with the material intermittently; sustain the force once begun.

Glass-Filled PEEK (GF30) — Higher Stiffness, Higher Tool Wear

Adding 30% glass reinforcement to the PEEK matrix greatly improves stiffness and compressive strength while additionally reducing thermal expansion- this is why GF30 is the standard choice when parts must locate dimensional stability under mechanical strain at elevated temperature. Equipment seats, valve components, and wafer-handling tooling found in the semiconductors world often specify glass filled PEEK machining for this reason.

Tool wear is the trade-off. Glass fibers are abrasive on cutting edges, and industry machining data consistently shows that reinforced PEEK grades reduce tool life by 50–70% compared to unfilled PEEK. Standard carbide end mills that last through a full production run on 450G stock may dull halfway through the same program on GF30. Polycrystalline diamond (PCD) or diamond-coated carbide tooling is the recommended choice for production volumes.

📐 Engineering Note

When machining GF30 peek, expect a 20-30% reduction in cutting speeds when compared to the recommended parameters for unfilled material. Feed rates can often be similar, as can the declared depth of cut, but for end milling it is advisable to limit depth to a maximum of 50% of tooling diameter to limit the chip load and heat generation. Surface finish should be observed – as the tool dulls fiber pull-out results in a roughness value that can cause rejection before dimensional tolerances drift. Tool inspection can be scheduled at half the normal frequent intervals for unfilled PEEK.

GF30 also has different characteristics with respect to thin section machining. Internal stress concentrations introduced by the glass fibers heighten the chance of warping induced by aggressive machining. A gentle, multi-stage process of roughly removing 0.2-0.5 mm oversize stock, allowing the part to rest and stabilize then finishing produces more predictable results than aggressive single stage strategies.

Carbon Fiber PEEK (CF30) — Maximum Strength-to-Weight for Precision Parts

Carbon fiber reinforced peek (CF30) offers the highest specific strength of the PEEK series combined with athermal properties, with a conductivity about 3.5 times that of unfilled PEEK. That elevated conductivity enhances heat flow over the cutting zone during CNC machining, which in some conditions may actually improve the surface quality – albeit with the carbon fibers being more abrasive on tooling.

Where CF30 truly excels in precision CNC work comes from dimensional stability, since the carbon fiber reinforcement attenuates the coefficient of thermal expansion forces. PEEK components such as aerospace brackets, satellite assembly panels and instrument enclosures are commonly specified CF30 for this characteristic.

Machining attributes of CF30 peek are unchanged relative to GF30 – PCD tooling is recommended because carbon fibers cause comparable tool wear rates. However, the elevated thermal conductivity of CF30 can permits slightly increased cutting speeds relative to GF30 in a few common configurations, because the heat is more easily conducted away. Practical variation is not substantial enough to justify different screen values between these grades in most cases.

💡 Key Takeaway

CF30 is the PEEK grade to select when mechanical strength and dimensional stability both matter — particularly for structural applications in aerospace and medical devices where parts must maintain precise geometry across a wide temperature range. The cost premium over GF30 ($80–150 vs $60–120 per kg) is moderate, and the machining behavior is similar enough that tooling investment carries over between grades.

Bearing-Grade and Specialty PEEK — Low Friction, Conductive, and Food-Safe Variants

Beyond the performance benefits of reinforcing PEEK, additional proprietary grades of peek can be developed to meet specific functional needs. Bearing-grade PEEK incorporates PTFE as well as ground carbon and graphite flakes to obtain low coefficient of friction and high wear resistance for use in sliding contact applications. Literature has cited dry operation at 120, 000 PV (pressure velocity) limits for bearing-grade derivatives – approaching expected service limits for unfilled or fiber-reinforced material in some cases.

Conductive PEEK grades incorporate carbon black or carbon fiber to achieve low surface resistivity, making them suitable for semiconductor wafer handling, ESD-safe test sockets, and cleanroom fixtures where static discharge would damage components. Machining behavior is comparable to standard filled PEEK, though the carbon loading can affect chip characteristics.

Food-grade peek formulations meet all approvals required for direct food contact from the FDA; specialty high-temperature variants extend continuous-use grades far beyond the standard 250C limit in oil and gas downhole tools or autoclave environments.

Specialty Grade	Key Property	Typical Value	Primary Application
Bearing (PTFE-filled)	PV Limit (dry)	120,000 psi·ft/min	Bushings, thrust washers
ESD/Conductive	Surface Resistivity	10⁶–10⁹ ohm/sq	Wafer handling, test sockets
Food-Grade	FDA Compliance	21 CFR-compliant	Processing equipment, conveyors
High-Temperature	Continuous Service	260°C+	Downhole seals, autoclave parts

Medical-Grade PEEK (PEEK-OPTIMA) — Biocompatibility and Implant Requirements

Medical-grade PEEK occupies a category separate from industrial grades — not because the base polymer chemistry differs fundamentally, but because the purity, traceability, and regulatory documentation are on another level. PEEK-OPTIMA, produced by Invibio (a Victrex subsidiary), is the most widely used implantable-grade PEEK. Published clinical data from Invibio shows approximately 15 million implanted devices worldwide with zero material-related recalls over a 20-year track record.

Compliance covers ASTM F2026 (Standard Specification for PEEK Polymers for Surgical Implant Applications) and meets ISO 10993 biocompatibility requirements including cytotoxicity, sensitization, and implantation testing. Manufacturing takes place under ISO 13485:2016 certified quality systems with full supply chain control from monomer to finished polymer.

In processing cnc machining of medical-grade peek components like spinal fusion cages, dental abutments, trauma fixation plates and other applications, the processing environment is just as relevant as the cutting conditions applied. Good practice requires dedicated tooling (not shared with other polymers), nitrile gloves when handling special peek and HEPA-filtered laminar flow chambers above the processing area to avoid contamination. The implant-grade material itself behaves just like unfilled industrial PEEK in terms of feeds, speeds and chip formation; the challenge is in process control and documentation.

📐 Engineering Note

PEEK’s elastic modulus (3–4 GPa) is similar to that of human cortical bone. This fact directly translates into its application in load-bearing implants, as it can reduce the effects of stress shielding compared to titanium (modulus ~110 GPa). It is for this biomechanical reason that surgeons and device designers specify PEEK over metal for spinal interbody cages and craniomaxillofacial plates, even if their machining process is more complex and ultimately more expensive.

How to Select the Right PEEK Grade for Your CNC Machining Project

Selection of grade for peek machining applications should follow an evaluation process rather than take a chosen grade as the default. By following the checklist below, you can clearly identify the grade best suited to your application – and eliminate unsuitable options early.

PEEK Grade Selection Checklist

Operating temperature range. All peek grades are capable of withstanding continuous service at 250C. For higher operating temperatures specify a high-temp grade. If operating below 150 C then temperature is not a consideration – all grades have the same thermal properties.
Identify load profile. Static structural loads unfilled or CF30. Dynamic/cyclic loads unfilled (generates highest fatigue resistance). Heavy compressive loads GF30 or CF30.
Consider sliding contact or wear. Any bushing, seal or bearing surface bearing-grade peek with PTFE. Do not use unfilled or fiber-reinforced peek for dry-running sliding applications.
Regulatory considerations. Implantable medical device — PEEK-OPTIMA (ASTM F2026 + ISO 10993). Food contact — FDA 21 CFR approved grade. Semiconductor — ESD-safe conductive grade.
Define tolerance and stability needs. Tolerance and tolerance should be less than 0.05 mm CF30 (nominal lowest thermal-expansion) or blank without annealing. Custom tolerances for any grade with suitable machining practice.
Evaluate cost constraints. Production volume and per-part budget should be balanced against raw material cost ($40–800/kg depending on grade) plus tooling cost impact of reinforced grades (50–70% faster tool wear means higher per-part tooling expense).
Validate with a prototype machining run. Mill 2–3 test pieces before committing to production quantities. Check dimensional stability after 48 hours at ambient conditions, and confirm surface finish meets specification with your specific tooling and parameters.

Where special relevance to an application does not clearly dictate a dedicated reinforced grade, which are much more costly for CNC machining than unfilled or standard grades, unfilled peek (450G) generally provides the most cost-effective, reliable solution in the vast majority of industrial aerospace CNC processes. Design upgrades to GF30, CF30 or even bearing-grade PEEK therefore should be used for dramatic performance improvements only where justified by the precise application performance case.

For projects requiring precision tolerances on PEEK machined components across multiple grades, working with a machining partner experienced with PEEK reduces lead time and limits grade-related machining issues.

Frequently Asked Questions About PEEK Grades and Machining

Q: Is PEEK plastic expensive compared to other engineering plastics?

View Answer

Yes — industrial unfilled PEEK runs $40–90 per kilogram, roughly 5–10 times the cost of nylon ($5–15/kg) or acetal ($4–10/kg). Medical-grade PEEK-OPTIMA reaches $500–800/kg. The premium stems from synthesis complexity: polymerization demands high-temperature reactions with specialty monomers under tightly controlled conditions, and global production capacity remains limited. For most applications, the material cost pays for itself — parts that survive 250°C continuous service, repeated autoclave sterilization, and aggressive chemical environments without dimensional degradation.

Q: How machinable is PEEK compared to metals and other plastics?

View Answer

Unfilled PEEK machines more easily than titanium or stainless steel but needs more care than aluminum or commodity plastics like acetal. The primary challenge is heat — PEEK does not conduct heat away from the cutting zone efficiently, so aggressive parameters or dull tools cause the material to soften and smear rather than chip cleanly. Reinforced grades (GF30, CF30) add fiber abrasion that wears tooling faster, placing them on par with machining fiberglass composites. With sharp tooling and correct parameters, PEEK delivers excellent surface finishes.

Q: Can PEEK withstand chemicals and steam sterilization?

View Answer

PEEK resists most organic solvents, hydrocarbons, dilute acids, and bases at elevated temperatures. It is fully autoclavable — surviving repeated steam sterilization at 134°C without property loss. Notable exceptions are concentrated sulphuric acid and certain halogenated solvents, which can attack the polymer chain. For chemical processing applications, verify compatibility with your specific media, concentration, and temperature before specifying PEEK.

Q: Is any grade of PEEK biocompatible for permanent medical implants?

View Answer

Only PEEK manufactured specifically to implant-grade standards meets the regulatory requirements for permanent human implantation. PEEK-OPTIMA from Invibio holds ISO 10993 biocompatibility certification, ASTM F2026 compliance, and a clinical history spanning 15 million implanted devices. Standard industrial PEEK grades — even unfilled 450G with similar chemistry — lack the purity controls, lot traceability, and biological testing documentation required by regulatory authorities. Never substitute industrial PEEK for implant-grade material, regardless of mechanical property similarity.

Q: What CNC machining tolerances are achievable with PEEK?

View Answer

Standard PEEK CNC machining achieves ±0.025 mm (±0.001 inch) on critical dimensions. With stress-relief annealing between roughing and finishing, controlled ambient temperature, and CF30 grade selection (lowest thermal expansion), tolerances of ±0.02 mm are consistently attainable. Key variables include material grade, wall thickness, annealing protocol, and operating temperature. For tight-tolerance PEEK parts, specify the operating temperature range on your drawings — thermal expansion at 150°C versus room temperature can exceed machining tolerances if not factored into the design.

Q: Does glass-filled PEEK machine differently from unfilled PEEK?

View Answer

Significantly. The 30% glass fiber in GF30 PEEK is abrasive on cutting edges, reducing tool life by 50–70% compared to unfilled grades. Shops switching from unfilled to glass-filled should expect to change tooling roughly twice as often and should budget for PCD or diamond-coated inserts on production runs. Cutting speeds need a 20–30% reduction to manage wear, and chip evacuation becomes more important because loose fiber fragments can score the machined surface if not cleared promptly.

Q: Why does medical-grade PEEK cost so much more than industrial PEEK?

View Answer

That price gap ($500–800/kg medical vs $40–90/kg industrial) reflects regulatory burden, not chemistry differences. Medical-grade PEEK demands monomer-to-polymer supply chain traceability, manufacturing under ISO 13485 quality systems, extensive biocompatibility testing per ISO 10993, and lot-specific documentation that follows each batch through to the finished device. These controls add quality assurance costs at every production stage. The polymer base is similar, but the testing, documentation, and facility requirements needed for implantable use multiply the cost by roughly ten times.

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About This Analysis

This guide was compiled by the engineering team at Lecreator, a Shenzhen-based CNC machining facility that processes multiple PEEK grades across aerospace, medical device, and semiconductor applications. The material property data cited here draws from peer-reviewed NIH publications, ASTM standard specifications, and manufacturer technical documentation — cross-referenced against machining outcomes observed across thousands of PEEK parts produced since 2008.