PEEK vs Delrin for Machined Parts
Delrin is the easy, cheap precision plastic; PEEK is the high-temperature, chemical-resistant upgrade. Strength, service temperature, machinability, cost, wear, and water absorption — compared with real data.
IsoCNC Engineering Team
CNC Machining & DFM Engineers · Updated · 8 min read
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Quick Answer
Choose Delrin for low-friction, dimensionally stable mechanical parts — gears, bushings, slides, housings — at ordinary temperatures and a low price. Choose PEEK when the part must survive heat (to 250–260°C), steam, harsh chemicals, or biocompatible performance — but expect to pay roughly an order of magnitude more for the material. In one line: Delrin for everyday precision, PEEK for the environments that break Delrin.
The Everyday Plastic vs the Performance Polymer
Delrin and PEEK both machine into precise plastic parts, but they live on opposite ends of the engineering-plastics spectrum. Delrin (acetal/POM) is the workhorse — easy to machine, dimensionally stable, low friction, and cheap. PEEK is the performance polymer — a semi-crystalline thermoplastic that holds its strength to 250–260°C and shrugs off chemicals, steam, and wear that would destroy Delrin. The decision is almost never “which is better.” It is whether your part needs to survive an environment Delrin cannot, and whether it is worth paying an order of magnitude more for the material.
PEEK vs Delrin at a Glance
The numbers that drive the decision:
| Property | Delrin (Acetal/POM) | PEEK |
|---|---|---|
| Tensile strength | 69–80 MPa | 100–115 MPa |
| Flexural modulus | 2.8–3.5 GPa | 3.6–4.1 GPa |
| Density | 1.41 g/cm³ | 1.30–1.33 g/cm³ |
| Continuous service temp | 82–90°C (120°C short-term) | 250–260°C |
| Chemical resistance | Good vs fuels/oils; weak vs acids/bases | Broad — acids, bases, solvents, steam |
| Machinability | Excellent, easiest | Good, more demanding |
| Friction (coef.) | 0.2–0.3 | 0.1–0.2 |
| Water absorption | ~0.2–0.3% | ~0.05–0.2% |
| Relative cost | Low ($5–15/kg) | High ($90–400/kg) |
| Typical uses | Gears, bushings, slides, housings | Aerospace, medical, steam, high-temp |
Read the temperature and cost rows together — that pair is the whole decision. PEEK costs roughly 20 times Delrin per kilogram, and the only thing that justifies it is the 250°C-versus-90°C service gap.
Temperature and Chemicals: Where PEEK Earns Its Price
The clearest separator is heat. Delrin is rated for continuous service around 82–90°C, with short-term excursions to roughly 120°C. Push past that and it softens, distorts, and loses its mechanical properties. PEEK runs continuously at 250–260°C — hot enough for autoclave sterilization, steam service, and engine-adjacent components. Chemically, the same story: Delrin handles fuels, oils, and neutral solvents well but is attacked by strong acids, strong bases, and oxidizing agents, and it hydrolyzes under prolonged hot water or steam. PEEK resists most acids, bases, solvents, and hydrocarbons, and holds up in steam where Delrin degrades.
The practical rule: if the part sees heat, steam, sterilization, or aggressive chemistry, Delrin is out and PEEK is in. If it lives at room temperature in a clean mechanical environment, Delrin is the sensible choice.
Machinability and Precision: Delrin Is the Easy One
For the machinist, Delrin is about as good as plastics get: excellent machinability, clean chip formation, good dimensional stability, and a good surface finish straight off the machine. PEEK also machines well but is more demanding — its higher heat resistance and tougher behavior mean slower speeds, sharper tools, and more care. Both hold tight tolerances, but Delrin is the faster, lower-risk, cheaper choice for a general precision plastic part. If your drawing just says “plastic bushing” or “gear,” Delrin is almost certainly the answer; PEEK only enters when the spec adds “high temperature” or “chemical resistance.” If PEEK wins on environment, our PEEK machining guide covers grades, annealing, and tooling.
Wear and Water: Close, with PEEK Ahead
Both are low-friction, wear-friendly plastics — that is why they show up in bearings and slides. PEEK runs a slightly lower coefficient of friction (about 0.1–0.2 versus Delrin’s 0.2–0.3) and is generally positioned as the stronger high-performance wear material. On water, PEEK also has the edge — roughly 0.05–0.2% absorption versus Delrin’s 0.2–0.3% — which matters when dimensional stability in humid or wet environments is a requirement. The differences are real but modest; they matter most in precision sliding applications where a few microns of swell or a fraction of friction coefficient changes performance.
Cost: An Order of Magnitude
This is the number that ends most conversations. Delrin stock runs about $5–15/kg; PEEK runs $90–400/kg — roughly twenty times more. That gap is the reason PEEK is never a default material: you specify it because the part must survive heat, steam, chemicals, or biocompatible service, not because it sounds premium. The machining cost difference is smaller — both cut well — but the raw material alone pushes a PEEK part into a different price tier. If a part can live as Delrin, it should; PEEK only earns its premium when the environment demands it.
For the full plastic-selection picture, see our Delrin vs nylon comparison and the plastic CNC machining material page.
How to Choose
Choose Delrin for gears, bushings, slides, pulleys, and precision housings at moderate temperatures — the low-friction, dimensionally stable, cost-effective default.
Choose PEEK for aerospace, medical and biocompatible parts, chemical-processing equipment, and steam or autoclave environments where heat and chemical resistance are non-negotiable.
When in doubt, ask what the part must survive. If the answer is “room temperature, clean, mechanical,” Delrin wins on cost and machinability. If the answer involves heat, steam, or chemicals, PEEK is the only one of the two that survives.
FAQ
Which is stronger, PEEK or Delrin?
PEEK. Its tensile strength of 100–115 MPa beats Delrin’s 69–80 MPa, and its flexural modulus of 3.6–4.1 GPa edges out Delrin’s 2.8–3.5 GPa. But strength is rarely why people choose between them — the real difference is temperature, where PEEK’s 250–260°C continuous service dwarfs Delrin’s 82–90°C.
What is the temperature limit of Delrin vs PEEK?
Delrin (acetal) is rated for continuous service around 82–90°C, with short-term excursions to roughly 120°C. PEEK runs to 250–260°C continuous. If the part sees heat, steam, or autoclave sterilization, that gap alone decides the material — Delrin simply cannot survive where PEEK is comfortable.
Is PEEK worth the extra cost over Delrin?
Only when the environment demands it. Delrin runs about $5–15/kg while PEEK runs $90–400/kg — an order of magnitude more — so PEEK is never a default. Choose PEEK for high temperature, harsh chemicals, steam, or biocompatible high-performance parts; choose Delrin for low-friction, dimensionally stable mechanical parts at moderate temperatures and ordinary cost.
Which machines better, PEEK or Delrin?
Both machine well, but Delrin is the easier of the two — excellent machinability, clean chip formation, and good dimensional stability. PEEK machines well but is more demanding because of its higher heat resistance and tougher behavior. For a general low-risk precision plastic part, Delrin is the faster, cheaper, easier choice.
Is PEEK biocompatible?
Implant-grade PEEK (per ASTM F2026) is used in medical applications including spinal implants, and it withstands steam and autoclave sterilization that Delrin cannot. Delrin is not the choice for implantable or high-temperature sterilizable parts. For the medical-material picture, see our medical device machining guide.
PEEK vs Delrin vs Nylon — how do they compare?
Think of it as three tiers. Nylon is the tough, moisture-absorbing generalist; Delrin is the low-friction, dimensionally stable precision plastic; and PEEK is the high-temperature, chemical-resistant performance polymer. Our Delrin vs Nylon guide covers the first two tiers in depth, and this page covers the Delrin-to-PEEK jump.
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Delrin and PEEK, Machined In-House
IsoCNC machines both plastics daily — from Delrin gears and bushings to PEEK medical and aerospace components — with tight tolerances and clean finishes. Send the drawing; an engineer reviews every RFQ, typically within 1–2 business days.