PEEK vs Delrin vs Nylon: Which Plastic for CNC Parts? (2026)

Q: Is PEEK stronger than Delrin and nylon?

Yes. PEEK has a tensile strength of approximately 14,500 psi (100 MPa) compared to Delrin at 10,000 psi (69 MPa) and nylon 6/6 at 11,800 psi (82 MPa). More importantly, PEEK retains a much larger fraction of its strength at elevated temperatures — it maintains useful mechanical properties up to 480 °F (250 °C) continuously, while Delrin softens at 180 °F (82 °C) and nylon 6/6 at 220 °F (105 °C). At room temperature, the strength difference between the three is modest; the real separation is thermal and chemical performance.

Q: Why is PEEK so much more expensive than Delrin or nylon?

PEEK resin costs $40–80/lb compared to $2–4/lb for acetal and $1.50–3/lb for nylon 6/6. The price premium stems from PEEK's complex polymerization process (requires 4,4'-difluorobenzophenone and hydroquinone reacted at high temperature under inert atmosphere), limited global production capacity (Victrex, Solvay, and Evonik are the main producers), and the high extrusion temperatures needed to form stock shapes. In rod form, PEEK typically runs $180–300/ft for 2 in. diameter versus $15–25/ft for Delrin and $10–20/ft for nylon. The material cost alone can make a PEEK part 7–20× more expensive than the same geometry in Delrin.

Q: Can nylon replace Delrin for CNC machined parts?

In some applications, yes — but moisture absorption is the limiting factor. Nylon 6/6 absorbs 1.2–1.5% moisture in 24 hours of immersion (vs. 0.20% for Delrin), which causes dimensional swelling of 1–2% and reduces mechanical properties by 10–20% in humid environments. For precision parts that require tight tolerances (±0.001–0.002 in.) or operate in high-humidity environments, Delrin is the safer choice. Nylon is preferred when higher impact toughness, lower density, or lower material cost is the priority — and when the humidity environment is controlled or the tolerance is looser (±0.003–0.005 in.).

Q: Which plastic is easiest to CNC machine?

Delrin (acetal) is widely considered the easiest engineering plastic to machine. It produces short, well-broken chips, holds the tightest tolerances (±0.001 in. / 0.025 mm achievable), achieves the finest surface finish (Ra 16–32 μin. / 0.4–0.8 μm), and generates minimal tool wear. Nylon machines well but produces long stringy chips that require chip-breaker tool geometry and can wrap around the spindle. PEEK machines well with carbide tooling but generates more heat due to its higher strength and lower thermal conductivity — air blast cooling is essential to prevent surface glazing.

Q: Which plastic should I use for medical device components?

For medical devices, the choice depends on sterilization method and regulatory requirements. If the part must survive autoclave sterilization (270 °F / 132 °C), PEEK is the only option — it is also biocompatible per ISO 10993, USP Class VI, and available in implant-grade (PEEK-OPTIMA). For devices sterilized by EtO or gamma radiation at ambient temperatures, Delrin 150 is FDA-compliant (21 CFR 177.2480), dimensionally stable, and 10–15× cheaper than PEEK. Nylon is generally avoided for medical devices due to moisture absorption, which causes dimensional instability after sterilization and during use in wet clinical environments.

Q: What tolerances can you hold on PEEK, Delrin, and nylon?

Achievable CNC tolerances depend on the material and feature geometry. Delrin: ±0.001 in. (0.025 mm) on precision features due to low moisture uptake and high dimensional stability. PEEK: ±0.002 in. (0.05 mm) standard — comparable to Delrin but requires slower speeds to manage heat; stress-relieving before final machining improves results. Nylon 6/6: ±0.002–0.003 in. (0.05–0.08 mm) achievable, but moisture-driven swelling can exceed 0.005 in. on large cross-sections in uncontrolled environments. For all three, anneal or stress-relieve the stock before final machining for tightest results.

Q: Can I 3D print PEEK, Delrin, or nylon instead of CNC machining?

Nylon is the most established 3D printing material of the three — available in SLS (PA12, PA11), MJF (PA12), and FDM (nylon 6, nylon 12) with typical tolerances of ±0.005–0.010 in. (0.13–0.25 mm). PEEK can be FDM-printed on high-temperature printers (400 °C+ nozzle, 150 °C+ chamber) but print quality varies and material properties reach only 60–80% of CNC-machined PEEK. Delrin (acetal) cannot be reliably 3D printed — it warps severely during FDM and is not available in powder-bed processes. For prototyping, SLS nylon is a cost-effective proxy; for production parts requiring full material properties, CNC machining remains the standard for all three.

Q: Does nylon swell from moisture and affect dimensions?

Yes. Nylon 6/6 absorbs 1.2–1.5% moisture by weight in 24 hours of water immersion and reaches equilibrium moisture content of 2.5–3.0% in 50% relative humidity. This causes linear dimensional growth of 1–2% (approximately 0.010–0.020 in. per inch), which is significant for precision parts. The moisture also acts as a plasticizer, reducing tensile strength by 10–20% and stiffness by 15–30%. Dry-as-molded nylon is stiffer and stronger but brittle; conditioned nylon is tougher but larger. For parts requiring dimensional stability, condition nylon to equilibrium before final machining, or use Delrin or PEEK instead.

Quick Answer

Use Delrin (acetal) for precision wear parts, bushings, and gears where dimensional stability and low friction matter. Use nylon 6/6 for impact-loaded structural parts and weight-sensitive applications where cost is a priority. Use PEEK only when the application demands continuous service above 200 °F (93 °C), autoclave sterilization, or broad chemical resistance — its 7–20× cost premium is only justified when the other two materials physically cannot survive the environment.

The Three Materials

Why These Three Plastics?

PEEK, Delrin, and nylon 6/6 cover the performance spectrum for CNC-machined engineering plastics. They share one trait — all three machine well on standard CNC equipment — but differ dramatically in temperature resistance, chemical compatibility, dimensional stability, and cost. Understanding the trade-offs prevents two common mistakes: over-specifying PEEK when Delrin would suffice (wasting money) and under-specifying nylon when the application demands Delrin or PEEK (causing field failures).

PEEK

Polyether Ether Ketone

Strengths

Highest strength and stiffness. Continuous service to 480 °F (250 °C). Broad chemical resistance. Autoclave-safe. Biocompatible grades available (PEEK-OPTIMA).

Limits

7–20× material cost premium. Moderate machinability — requires carbide tooling and careful heat management.

$180–300/ft (2 in. dia rod)

Delrin (Acetal / POM)

Polyoxymethylene — Homopolymer (Delrin) or Copolymer

Strengths

Lowest friction (0.20–0.35). Tightest CNC tolerances (±0.001 in.). Excellent chip formation. Dimensionally stable (0.20% water absorption). FDA-compliant grades.

Limits

Max service temp 180 °F (82 °C). Flammable (HB rated). Attacked by strong acids and oxidizers.

$15–25/ft (2 in. dia rod)

Nylon 6/6

Polyamide 6/6 (PA66)

Strengths

Highest impact toughness. Lightest of the three (1.14 g/cm³). Lowest material cost. Good fatigue resistance. Self-extinguishing (V-2).

Limits

High moisture absorption (1.2–1.5%) causes 1–2% dimensional swelling. Properties degrade in wet environments. Stringy chips during machining.

$10–20/ft (2 in. dia rod)

Head-to-Head Data

Mechanical & Thermal Properties Compared

All values are for unfilled, natural-color grades at room temperature and dry-as-molded condition. Filled grades (glass fiber, carbon fiber, PTFE) modify these properties significantly. For acetal-specific deep dives, see the acetal (POM/Delrin) guide.

Property	PEEK	Delrin (Acetal)	Nylon 6/6
Tensile Strength	14,500 psi (100 MPa)	10,000 psi (69 MPa)	11,800 psi (82 MPa)
Flexural Modulus	595,000 psi (4.1 GPa)	420,000 psi (2.9 GPa)	410,000 psi (2.8 GPa)
Elongation at Break	30–50%	25–75%	15–80%
Continuous Service Temp	480 °F (250 °C)	180 °F (82 °C)	220 °F (105 °C)
Deflection Temp (264 psi)	320 °F (160 °C)	185 °F (85 °C)	194 °F (90 °C)
Coefficient of Friction (dry)	0.35–0.45	0.20–0.35	0.30–0.45
Water Absorption (24 hr)	0.10%	0.20%	1.2–1.5%
Chemical Resistance	Broad (acids, bases, solvents, hydrocarbons)	Good (weak acids, bases, fuels; not strong acids)	Moderate (attacked by strong acids, absorbs moisture)
Inherent Flame Rating	V-0 (UL 94)	HB (flammable)	V-2 (self-extinguishing)
Density	0.047 lb/in³ (1.30 g/cm³)	0.051 lb/in³ (1.41 g/cm³)	0.041 lb/in³ (1.14 g/cm³)

Sources: MatWeb, Ensinger data sheets, Victrex PEEK 450G TDS, DuPont Delrin 150 TDS, BASF Ultramid A3K TDS. Values are typical; confirm with your resin supplier for the specific grade.

Environment Performance

Temperature Limits & Chemical Resistance

Temperature and chemical exposure are the two factors that most often force the material decision. If the part operates below 180 °F (82 °C) in a chemically benign environment, the choice is between Delrin and nylon based on mechanical requirements and cost. The moment you cross 200 °F or encounter aggressive chemicals, PEEK becomes the only viable option.

PEEK: the high-temperature champion

Continuous service to 480 °F (250 °C). Withstands autoclave sterilization at 270 °F (132 °C) with no dimensional change. Resists virtually all common solvents, acids (except concentrated H₂SO₄), bases, and hydrocarbons. The go-to material when thermal or chemical requirements disqualify the other two.

Delrin: stable up to 180 °F (82 °C)

Begins to soften and creep above 180 °F (82 °C). Good resistance to fuels, weak acids, bases, and common solvents. Attacked by strong mineral acids (HCl, H₂SO₄) and strong oxidizers. No formaldehyde off-gassing at normal service temperatures but may produce formaldehyde if burned — avoid flood coolant during machining as a precaution.

Nylon 6/6: moderate heat, moisture-sensitive

Service to 220 °F (105 °C) in dry conditions, but strength drops 10–20% when moisture-saturated. Attacked by strong acids (formic acid, phenol, ZnCl₂ solutions). Absorbs 1.2–1.5% moisture in 24 hr immersion — dimensional growth of 1–2% and plasticization of the polymer backbone.

Decision rule: temperature threshold

Below 180 °F → Delrin or nylon (cost-driven choice). 180–220 °F → Nylon 6/6 (if dry environment and moderate tolerance OK). Above 220 °F → PEEK is the only option. Autoclave sterilization → PEEK only. Chemical exposure → check PEEK compatibility chart first, then Delrin, then nylon.

CNC Machinability

CNC Machinability & Achievable Tolerances

All three materials machine on standard 3-axis CNC mills and lathes, but they behave differently at the tool tip. Delrin is the gold standard for CNC plastic machinability; nylon and PEEK require more attention to chip management and heat control.

Factor	PEEK	Delrin (Acetal)	Nylon 6/6
Machinability Rating	Moderate	Excellent	Good
Typical Surface Finish (Ra)	32–63 μin. (0.8–1.6 μm)	16–32 μin. (0.4–0.8 μm)	32–63 μin. (0.8–1.6 μm)
Achievable Tolerance	±0.002 in. (±0.05 mm)	±0.001 in. (±0.025 mm)	±0.002–0.003 in. (±0.05–0.08 mm)
Tool Wear	Moderate–High (use carbide)	Low (HSS or carbide)	Low–Moderate (carbide preferred)
Chip Formation	Short, well-broken chips	Excellent chip-breaking	Long stringy chips (use chip-breaker geometry)
Coolant	Air blast or light mist	Air blast (avoid flood — formaldehyde risk)	Air blast or flood coolant
Dimensional Stability	High (low moisture uptake)	High (low moisture, low creep)	Low — swells 1–2% with humidity
Typical Material Cost (rod, 2 in. dia)	$180–300/ft	$15–25/ft	$10–20/ft

Cost Reality

Material Cost: The 7–20× PEEK Premium

Material cost is the dominant cost driver for plastic CNC parts — unlike metals where machining time often exceeds material cost. On a typical 3×3×1 in. bracket, the material alone for PEEK is $40–80 vs $3–8 for Delrin or nylon.

Machining cost for all three is comparable on standard CNC equipment ($75–125/hr). PEEK may require 10–20% longer cycle times due to slower speeds and carbide tooling wear, but the material cost gap dwarfs the machining cost difference. For strategies to reduce per-part cost regardless of material, see our guide to reducing CNC machining cost.

Don’t spec PEEK “just in case”

The most common over-spec mistake: calling out PEEK for a part that operates at room temperature in a benign chemical environment. If the application does not require sustained heat above 200 °F, autoclave sterilization, or broad chemical resistance, Delrin or nylon provides equivalent mechanical performance at 7–20× lower material cost. Prototype in the cheaper material first; switch to PEEK only when testing proves the lower-cost option fails.

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Use This Material When…

Application Decision Table

Match your design scenario to the recommended material. Each row explains the reasoning and gives typical applications in robotics, medical devices, and industrial automation.

Design Scenario	Recommended Material	Why	Typical Applications
Bushings, bearings, and wear pads (dry sliding)	Delrin (acetal)	Lowest coefficient of friction (0.20–0.35), self-lubricating, dimensionally stable, and 7–12× cheaper than PEEK. Acetal is the standard choice for dry bearing applications up to 180 °F (82 °C).	Robotics: joint bushings, conveyor guides, cable management slides
Precision gears and cams	Delrin (acetal)	Excellent dimensional stability under cyclic loading, low moisture absorption, and the tightest CNC tolerances of the three (±0.001 in.). Nylon gears swell with humidity and lose mesh precision.	Robotics: spur gears, worm drives. Medical: sterilizable drive mechanisms
High-temperature environments (>200 °F / 93 °C)	PEEK	Only PEEK maintains strength above 200 °F. Delrin softens at 180 °F; nylon 6/6 at 220 °F. For sustained operation above 250 °F, PEEK is the only unfilled option in this comparison.	Semiconductor: wafer handling fixtures. EV: battery module insulators
Autoclave or steam sterilization (270 °F / 132 °C)	PEEK	PEEK withstands repeated autoclave cycles at 270 °F (132 °C) without dimensional change. Delrin degrades above 250 °F. Nylon absorbs moisture during steam sterilization and swells.	Medical devices: surgical instrument handles, sterilization trays, implant-grade guides
Aggressive chemical exposure (concentrated acids, ketones)	PEEK	PEEK resists virtually all common chemicals except concentrated sulfuric acid and some halogenated solvents. Delrin is attacked by strong acids (pH <4). Nylon is dissolved by phenol and formic acid.	Semiconductor: chemical delivery components. Industrial: pump impellers, valve seats
Structural parts requiring high impact toughness	Nylon 6/6	Nylon 6/6 has the highest impact strength of the three and absorbs energy through plastic deformation. Use for snap-fit housings, impact-loaded brackets, or parts that must survive drop tests.	Robotics: end-effector housings, cable chain links. Consumer: enclosure clips
Lightweight parts (density-critical)	Nylon 6/6	At 1.14 g/cm³, nylon 6/6 is 12% lighter than PEEK and 19% lighter than Delrin. For weight-sensitive robotic end-of-arm tooling or drone components, nylon provides the best strength-to-weight ratio.	Robotics: lightweight gripper jaws, EOAT mounting plates
FDA food contact or USP Class VI compliance	Delrin (acetal) or PEEK	Delrin 150 and certain PEEK grades meet FDA 21 CFR 177.2480 and USP Class VI. Nylon 6/6 is not inherently FDA-compliant due to caprolactam extraction. Always verify the specific grade with the resin supplier.	Medical: fluid pathway connectors. Food: conveyor components
Budget-constrained prototypes (material cost matters)	Nylon 6/6 or Delrin	Nylon rod is $10–20/ft; Delrin $15–25/ft; PEEK $180–300/ft. For functional prototypes where material performance is adequate, nylon or Delrin cuts material cost by 7–20× versus PEEK. Switch to PEEK only when thermal or chemical requirements demand it.	All industries: first-run prototypes, fit-check samples, pre-production validation

Industry Focus

Medical Device & Robotics Applications

MakerStage’s two primary customer segments — medical device and robotics teams — both rely heavily on engineering plastics. The material choice maps directly to regulatory requirements for medical and to performance/cost trade-offs for robotics.

Medical devices

Autoclave-sterilized surgical instruments → PEEK (PEEK-OPTIMA for implant contact)
EtO-sterilized disposable guides / fixtures → Delrin 150 (FDA 21 CFR 177.2480)
Fluid pathway connectors (non-implant) → Delrin or PEEK depending on chemical exposure
Sterilization tray inserts → PEEK for autoclave; Delrin for EtO/gamma

Nylon is generally avoided for medical devices due to moisture absorption causing dimensional instability after sterilization.

Robotics

Joint bushings and sleeve bearings → Delrin (low friction, wear resistance)
Lightweight gripper jaws and EOAT plates → Nylon 6/6 (lowest density, good impact)
High-temp motor insulators and sensor mounts → PEEK (thermal stability)
Cable management slides and guides → Delrin (low friction, snap-fit retention)

For most room-temperature robotics applications, Delrin covers 70–80% of plastic part needs. PEEK is reserved for motor-adjacent hot zones.

For detailed acetal-vs-nylon and acetal-vs-PEEK head-to-head comparisons with filled-grade data, see acetal vs nylon and acetal vs PEEK. For CNC-specific machining guidance, see CNC machining acetal.

Common Questions

PEEK vs Delrin vs Nylon FAQ

Is PEEK stronger than Delrin and nylon?

Yes. PEEK has a tensile strength of approximately 14,500 psi (100 MPa) compared to Delrin at 10,000 psi (69 MPa) and nylon 6/6 at 11,800 psi (82 MPa). More importantly, PEEK retains a much larger fraction of its strength at elevated temperatures — it maintains useful mechanical properties up to 480 °F (250 °C) continuously, while Delrin softens at 180 °F (82 °C) and nylon 6/6 at 220 °F (105 °C). At room temperature, the strength difference between the three is modest; the real separation is thermal and chemical performance.

Why is PEEK so much more expensive than Delrin or nylon?

PEEK resin costs $40–80/lb compared to $2–4/lb for acetal and $1.50–3/lb for nylon 6/6. The price premium stems from PEEK's complex polymerization process (requires 4,4'-difluorobenzophenone and hydroquinone reacted at high temperature under inert atmosphere), limited global production capacity (Victrex, Solvay, and Evonik are the main producers), and the high extrusion temperatures needed to form stock shapes. In rod form, PEEK typically runs $180–300/ft for 2 in. diameter versus $15–25/ft for Delrin and $10–20/ft for nylon. The material cost alone can make a PEEK part 7–20× more expensive than the same geometry in Delrin.

Can nylon replace Delrin for CNC machined parts?

In some applications, yes — but moisture absorption is the limiting factor. Nylon 6/6 absorbs 1.2–1.5% moisture in 24 hours of immersion (vs. 0.20% for Delrin), which causes dimensional swelling of 1–2% and reduces mechanical properties by 10–20% in humid environments. For precision parts that require tight tolerances (±0.001–0.002 in.) or operate in high-humidity environments, Delrin is the safer choice. Nylon is preferred when higher impact toughness, lower density, or lower material cost is the priority — and when the humidity environment is controlled or the tolerance is looser (±0.003–0.005 in.).

Which plastic is easiest to CNC machine?

Delrin (acetal) is widely considered the easiest engineering plastic to machine. It produces short, well-broken chips, holds the tightest tolerances (±0.001 in. / 0.025 mm achievable), achieves the finest surface finish (Ra 16–32 μin. / 0.4–0.8 μm), and generates minimal tool wear. Nylon machines well but produces long stringy chips that require chip-breaker tool geometry and can wrap around the spindle. PEEK machines well with carbide tooling but generates more heat due to its higher strength and lower thermal conductivity — air blast cooling is essential to prevent surface glazing.

Which plastic should I use for medical device components?

For medical devices, the choice depends on sterilization method and regulatory requirements. If the part must survive autoclave sterilization (270 °F / 132 °C), PEEK is the only option — it is also biocompatible per ISO 10993, USP Class VI, and available in implant-grade (PEEK-OPTIMA). For devices sterilized by EtO or gamma radiation at ambient temperatures, Delrin 150 is FDA-compliant (21 CFR 177.2480), dimensionally stable, and 10–15× cheaper than PEEK. Nylon is generally avoided for medical devices due to moisture absorption, which causes dimensional instability after sterilization and during use in wet clinical environments.

What tolerances can you hold on PEEK, Delrin, and nylon?

Achievable CNC tolerances depend on the material and feature geometry. Delrin: ±0.001 in. (0.025 mm) on precision features due to low moisture uptake and high dimensional stability. PEEK: ±0.002 in. (0.05 mm) standard — comparable to Delrin but requires slower speeds to manage heat; stress-relieving before final machining improves results. Nylon 6/6: ±0.002–0.003 in. (0.05–0.08 mm) achievable, but moisture-driven swelling can exceed 0.005 in. on large cross-sections in uncontrolled environments. For all three, anneal or stress-relieve the stock before final machining for tightest results.

Can I 3D print PEEK, Delrin, or nylon instead of CNC machining?

Nylon is the most established 3D printing material of the three — available in SLS (PA12, PA11), MJF (PA12), and FDM (nylon 6, nylon 12) with typical tolerances of ±0.005–0.010 in. (0.13–0.25 mm). PEEK can be FDM-printed on high-temperature printers (400 °C+ nozzle, 150 °C+ chamber) but print quality varies and material properties reach only 60–80% of CNC-machined PEEK. Delrin (acetal) cannot be reliably 3D printed — it warps severely during FDM and is not available in powder-bed processes. For prototyping, SLS nylon is a cost-effective proxy; for production parts requiring full material properties, CNC machining remains the standard for all three.

Does nylon swell from moisture and affect dimensions?

Yes. Nylon 6/6 absorbs 1.2–1.5% moisture by weight in 24 hours of water immersion and reaches equilibrium moisture content of 2.5–3.0% in 50% relative humidity. This causes linear dimensional growth of 1–2% (approximately 0.010–0.020 in. per inch), which is significant for precision parts. The moisture also acts as a plasticizer, reducing tensile strength by 10–20% and stiffness by 15–30%. Dry-as-molded nylon is stiffer and stronger but brittle; conditioned nylon is tougher but larger. For parts requiring dimensional stability, condition nylon to equilibrium before final machining, or use Delrin or PEEK instead.

Related Resources

Acetal (POM / Delrin) Guide

Complete guide: grades, properties, machining, applications

Acetal vs PEEK

Head-to-head: when is PEEK worth the cost premium?

Acetal vs Nylon

Wear, moisture, cost, and when each wins

CNC Machining Acetal

Speeds, feeds, tooling, and DFM rules for POM

CNC Machining PEEK

Grades, annealing, tolerances, and DFM for PEEK parts

Material Selection Guide

Framework for choosing metals and plastics

Reduce CNC Machining Cost

12 strategies to lower per-part cost

CNC Parts in PEEK, Delrin, or Nylon — Free DFM Review

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