What Is Acetal (POM/Delrin)? Engineer's Guide (2026)

Q: What is the difference between Delrin and acetal?

Delrin is a trade name owned by DuPont (now Celanese) for their acetal homopolymer (POM-H). "Acetal" is the generic material family name covering both homopolymer and copolymer grades. All Delrin is acetal POM-H, but not all acetal is Delrin — other manufacturers produce equivalent homopolymer and copolymer grades under different brand names.

Q: What is POM material used for?

POM (polyoxymethylene) is used for precision mechanical parts requiring low friction, tight tolerances, and dimensional stability: gears, bushings, bearings, rollers, valve bodies, pump components, food processing parts, and electrical connectors. Its machinability — clean chips, tight tolerances, no coolant required — makes it the first-choice engineering plastic for CNC-machined precision parts.

Q: Is acetal stronger than nylon?

Acetal has higher tensile modulus (stiffness) than nylon and far better dimensional stability because it absorbs less than 0.25% moisture versus 1.5% (PA12, equilibrium) to 8.5% (PA6, fully saturated) depending on nylon grade and humidity exposure. However, nylon typically has higher impact toughness. The correct comparison depends on the application: acetal wins for precision sliding fits; nylon wins for high-impact, high-temperature applications.

Q: What temperature can acetal handle?

Acetal (POM) has a continuous service temperature of approximately 90–100°C (194–212°F) for unfilled grades. Short-term peak exposures up to 120°C are tolerable. Above 100°C continuous, POM begins to creep under load and loses significant stiffness. For applications above 120°C, consider PEEK (250°C continuous) or other high-performance polymers.

Q: Does acetal absorb water?

Acetal absorbs very little moisture — typically less than 0.25% at 50% RH equilibrium versus 2.5–3% for PA6 nylon at the same conditions (or up to 8.5% when fully saturated by immersion). This low moisture absorption is the primary reason acetal maintains tight dimensional tolerances in humid environments. Precision bearing and gear applications where nylon would swell dimensionally are ideal acetal applications.

Q: Can acetal be CNC machined?

Acetal (POM) is one of the most machinable engineering plastics. It produces clean, short chips at high speeds, requires no coolant for most operations, holds tight tolerances (±0.001 in readily achievable), and gives excellent surface finish with standard carbide tooling. Its predictable chip behavior makes it far easier to machine than most nylons or polycarbonate.

Q: Is Delrin food safe?

Natural (white/ivory) Delrin and natural-grade acetal POM-H are compliant with FDA 21 CFR 177.2470 for food contact applications. Black acetal typically uses carbon black pigments that may not meet FDA requirements — always verify the specific grade with the material supplier. For confirmed FDA-grade acetal, specify "natural color, FDA-compliant grade" explicitly in your drawings.

Acetal Is the Default Engineering Plastic for Precision Sliding Parts.

If your part slides, rotates, or needs to hold a tight tolerance in a humid environment, acetal (POM) should be your first material candidate — not nylon, not polycarbonate. It absorbs virtually no moisture, machines like a dream, and delivers consistent dimensional stability that most other engineering plastics cannot match at room temperature. This guide covers everything you need to specify it correctly.

Section 1 of 6

What Is Acetal (POM)?

If you're specifying plastics for precision mechanical parts, acetal (POM) should be the first material on your shortlist — here's why. Acetal is a semi-crystalline (partially ordered molecular structure that gives it high stiffness and chemical resistance) thermoplastic built from repeating oxymethylene (–CH₂–O–) units. The formal IUPAC name is polyoxymethylene (POM). It belongs to the polyacetal family and is one of the strongest, stiffest, and most dimensionally stable commodity engineering plastics available.

Trade Names and Generics

Delrin®Homopolymer (POM-H)

Celanese (formerly DuPont)

The original acetal homopolymer; most engineers use "Delrin" generically

Celcon®Copolymer (POM-C)

Celanese

Celanese copolymer grade; good chemical resistance and no centerline porosity

Ultraform®Copolymer (POM-C)

BASF

BASF equivalent copolymer; widely available in rod and plate stock

Acetal / POM (generic)POM-H or POM-C

Multiple suppliers

Generic stock — specify homopolymer or copolymer grade explicitly on drawings

Why Engineers Choose Acetal

Dimensional stability

Absorbs <0.25% moisture versus 1.5% (PA12) to 8.5% (PA6, saturated) for nylon grades. Parts maintain specified dimensions in humid environments without swelling.

Natural lubricity

Low coefficient of friction (0.20–0.35 vs steel) without added lubricant. Ideal for gears, bushings, and cams running against metal.

Hardness and stiffness

Rockwell M80 hardness and 3,100 MPa tensile modulus — stiffer than most engineering plastics at room temperature.

Excellent machinability

Short, clean chips at high speeds. Holds ±0.001 in tolerances with standard carbide tooling. No coolant required for most operations.

Fatigue resistance

POM resists cyclic loading well — a key advantage in gear tooth root stress and snap-fit applications.

What Acetal Cannot Do

POM is susceptible to strong acids and oxidizing agents — it degrades rapidly in concentrated nitric, sulfuric, and hydrochloric acid. It also has poor UV resistance for outdoor long-term exposure without stabilizers, and softens above 100°C continuous service temperature. For elevated-temperature applications above 120°C, PEEK or PPS are the correct upgrade path.

Section 2 of 6

Acetal Grades: Homopolymer vs. Copolymer

When you call out acetal on a drawing, specifying homopolymer or copolymer is not optional — the wrong choice risks centerline porosity or unnecessary cost. The first decision in acetal specification is homopolymer (POM-H) or copolymer (POM-C). The structural difference is fundamental, not superficial, and drives real performance differences in thick sections and chemically aggressive environments.

Property	POM-H (Homopolymer)	POM-C (Copolymer)	Notes
Trade name example	Delrin® 150 (Celanese)	Celcon® M90, Ultraform®	Equivalent generics available from multiple suppliers
Tensile strength (UTS)	69 MPa (10 ksi)	62 MPa (9 ksi)	POM-H ~10% stronger in tension
Flexural modulus	2,900 MPa	2,550 MPa	POM-H stiffer — better for load-bearing precision parts
Hardness (Rockwell M)	M80	M76–M80	Essentially equivalent for most applications
Centerline porosity	Present in sections >25 mm	None	POM-H solidifies from outside in; cores can form voids in thick rod
Thermal stability	Good	Better	POM-C more resistant to thermal oxidative degradation — longer service life at elevated temps
Chemical resistance	Good	Better	POM-C copolymer backbone more resistant to alkalis and some organic solvents
Machinability	Excellent	Excellent	Essentially identical — both machine very well
FDA/food contact	Yes (natural grade)	Yes (natural grade)	Both available in FDA-compliant natural grades; verify specific grade
Typical stock form	Rod, plate, sheet	Rod, plate, sheet	Both widely available; POM-H slightly more common in the US market

Which Grade to Specify by Default

For most CNC machined parts under 25 mm (1 in) diameter or thickness, specify POM-H (Delrin homopolymer) — the slightly higher tensile strength and modulus give you a small design margin. For parts machined from rod or plate stock over 25 mm, or for parts in chemically aggressive or elevated-temperature environments, switch to POM-C (copolymer) to avoid centerline porosity and improve thermal stability. Read the full comparison in our Delrin vs. Acetal Copolymer guide.

Section 3 of 6

Full Mechanical Properties Reference

Before you finalize wall thicknesses or bearing loads in your design, confirm the actual numbers — datasheet values vary by grade and condition. All values for unfilled acetal at 23°C (73°F), per ASTM D638, D790, D256, and D785 unless noted. Properties degrade with temperature — see thermal section below.

Property	POM-H (Delrin 150)	POM-C (Copolymer)	Test Method
Density	1.42 g/cm³	1.41 g/cm³	ASTM D792
Tensile Strength (UTS)	69 MPa (10 ksi)	62 MPa (9 ksi)	ASTM D638
Tensile Modulus (Young's)	3,100 MPa (450 ksi)	2,690 MPa (390 ksi)	ASTM D638
Elongation at Break	40–75%	60–75%	ASTM D638
Flexural Strength	98 MPa (14.2 ksi)	89 MPa (12.9 ksi)	ASTM D790
Flexural Modulus	2,900 MPa (420 ksi)	2,550 MPa (370 ksi)	ASTM D790
Izod Impact (notched)	75–130 J/m	65–100 J/m	ASTM D256
Hardness (Rockwell M)	M80	M76–M80	ASTM D785
Hardness (Shore D)	D80	D80	ASTM D2240
Compressive Strength	127 MPa (18.4 ksi)	110 MPa (16 ksi)	ASTM D695
Coefficient of Friction (vs steel, dry)	0.20–0.35	0.25–0.35	ASTM D1894
Wear (Taber, H18, 1 kg)	6–12 mg/1000 cycles	8–14 mg/1000 cycles	ASTM D1044
Moisture Absorption (24 hr)	0.25%	0.22%	ASTM D570
Moisture Absorption (equilibrium)	0.90%	0.80%	ASTM D570
Thermal Conductivity	0.31 W/m·K	0.31 W/m·K	ASTM C177
CTE	110 µm/m·°C	110 µm/m·°C	ASTM D696
Continuous Service Temp	90–100°C	90–100°C	UL 746B
Melting Point	175°C (347°F)	165°C (329°F)	DSC
Dielectric Strength	19.7 kV/mm	19.7 kV/mm	ASTM D149
Volume Resistivity	>10¹⁵ Ω·cm	>10¹⁵ Ω·cm	ASTM D257

Section 4 of 6

Chemical Resistance

If your part contacts any fluid beyond clean water or light oil, verify acetal's chemical compatibility before committing — POM fails catastrophically in strong acids. Acetal has good chemical resistance to many fuels, lubricants, and solvents — but is attacked by strong acids and oxidizing agents. Know what your part will contact before specifying POM.

Chemical / Environment	Resistance	Notes
Aliphatic hydrocarbons (gasoline, diesel)	Excellent	Stable — POM used extensively in fuel system components
Alcohols (methanol, ethanol, isopropanol)	Good to Excellent	Slight swelling possible with methanol at elevated temperature
Mineral oils and greases	Excellent	No attack — POM commonly used with petroleum lubricants
Hydraulic fluids (mineral-based)	Excellent	Widely used in hydraulic sealing and valve components
Water (deionized or tap, room temp)	Excellent	Minimal moisture absorption; excellent dimensional stability
Mild detergents	Good	Acceptable for repeated wash-down service
Dilute acids (pH > 4)	Fair	Some degradation over time — test in application conditions
Concentrated mineral acids (HCl, H₂SO₄, HNO₃)	Poor — avoid	Rapid degradation; POM is not suitable for strong acid contact
Alkalis (NaOH, KOH)	Fair (POM-C better)	POM-H more sensitive than POM-C copolymer to strong alkalis
Oxidizing agents (bleach, H₂O₂ >3%)	Poor — avoid	Oxidative chain scission; use PVDF or PTFE for oxidizer contact
Aromatic solvents (toluene, xylene)	Fair	Slight swelling at elevated temperature; acceptable short-term contact
Ketones (MEK, acetone)	Fair	Slight swelling; generally acceptable for intermittent contact at room temp
Chlorinated solvents (methylene chloride, TCE)	Fair to Poor	Some attack possible at elevated temperatures; test before use
UV / outdoor weathering	Poor (unstabilized)	UV stabilized grades available; unfilled POM yellows and embrittles outdoors

Section 5 of 6

CNC Machinability

If you're quoting CNC plastic parts, acetal's machinability directly translates to lower cycle times, tighter tolerances, and reduced per-part cost. Acetal is widely considered the most machinable engineering plastic. It behaves more like aluminum than soft metal from a chip-making standpoint — and tolerances achievable rival those of aluminum alloys.

Turning (Lathe)

Surface speed: 300–600 SFM (90–180 m/min) with uncoated carbide
Feed rate: 0.003–0.010 in/rev (0.08–0.25 mm/rev) for finishing passes
Depth of cut: 0.050–0.150 in roughing; 0.005–0.020 in finishing
Sharp tools critical — dull tools generate heat and cause melting at the cutting edge
Dry cutting preferred; compressed air for chip clearing on deep bores
OD tolerances ±0.001 in readily achievable on good lathe setups

Milling (3-axis and 5-axis)

Spindle speed: 6,000–12,000 RPM with 1/2 in 2-flute carbide end mill
Feed rate: 100–200 in/min at 0.010–0.020 in per tooth
Shallow axial DOC (0.5× diameter) to avoid tool deflection and melting
Climb milling preferred for surface finish quality
No coolant needed for most operations; flood coolant can be used for deep pockets
Thin walls (< 0.060 in) require careful fixturing — POM deflects under clamping

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Section 6 of 6

Application Matrix

Before you lock your material selection, cross-check your application against this matrix — it covers where acetal excels and where it doesn't. Acetal excels in dry sliding, precision-tolerance, and dimensionally stable applications. Use this matrix to confirm fit-for-purpose before specifying.

Application	Verdict	Rationale
Plastic gears (low-to-medium load)	✓ Excellent	Natural lubricity, fatigue resistance, and dimensional stability make POM the default plastic gear material
Bushings and sleeve bearings (dry)	✓ Excellent	Low friction coefficient (0.20–0.35 vs steel), good wear resistance, holds bore dimensions in humidity
Cam followers and rollers	✓ Excellent	Resists wear and deformation under rolling contact; good for intermittent-duty applications
Valve bodies and pump components	✓ Good	Chemical resistance to fuels, oils, and mild fluids; verify against specific fluid contact list
Food contact parts (natural grade)	✓ Good (verify grade)	FDA 21 CFR 177.2470 compliance for natural grades; black grades not always food-safe
Medical device components	✓ Good (verify grade)	USP Class VI compliant grades available; excellent sterilization resistance to EtO
Precision jigs and fixtures	✓ Good	Dimensional stability in humidity better than nylon; used for precision gauge fixtures and locating pins
Electrical insulation (low voltage)	✓ Good	Excellent dielectric properties; common in connector housings and electrical standoffs
High-temperature applications (>120°C)	✗ Avoid	POM softens above 100°C continuous; upgrade to PEEK, PPS, or PTFE for elevated-temperature use
Strong acid contact (pH < 4)	✗ Avoid	Rapid degradation in strong mineral acids; use PVDF or PTFE for acid-contact applications
Outdoor UV-exposed parts (long-term)	✗ Avoid (unfilled)	UV-stabilized grades required; standard unfilled POM yellows and embrittles over months outdoors
High-impact shock loading	✗ Marginal	POM notched Izod is moderate; nylon or polycarbonate better for severe repeated impact

Explore the Full Acetal / POM / Delrin Content Series

Delrin vs. Acetal Copolymer: Homopolymer vs. Copolymer Compared — when POM-H beats POM-C and vice versa.
Acetal vs. Nylon: Which Engineering Plastic to Choose — moisture absorption, machinability, and application split.
Acetal vs. PEEK: When Is PEEK Worth the Cost Premium? — temperature limits, chemical resistance, and cost analysis.
CNC Machining Acetal (POM/Delrin): Speeds, Feeds, and Design Rules — full machining guide with DFM checklist.
Acetal CNC Tolerances: What's Achievable — turned OD, bored ID, flatness, thread classes.
Acetal Filled Grades: PTFE, Glass, Carbon Compared — specialty grades for gears, bearings, and high-wear applications.
Acetal Plastic Gears: Design Rules and Material Guide — module selection, PV limits, POM-on-steel pairing.
Acetal Bushings and Bearings: Low-Friction Design Guide — clearance fits, PV limits, shaft surface finish requirements.
FDA-Grade Acetal for Food and Medical Applications — FDA 21 CFR 177.2470, USP Class VI, and sterilization compatibility.
Acetal vs. UHMW Polyethylene: Stiffness, Wear, and Application Split — when UHMW's abrasion resistance outweighs acetal's stiffness.
Acetal vs. Polycarbonate: Lubricity vs. Impact and Transparency — choosing between low-friction precision and high-impact clarity.

Common Questions

Frequently Asked Questions

What is the difference between Delrin and acetal?

Delrin is a trade name owned by DuPont (now Celanese) for their acetal homopolymer (POM-H). "Acetal" is the generic material family name covering both homopolymer and copolymer grades. All Delrin is acetal POM-H, but not all acetal is Delrin — other manufacturers produce equivalent homopolymer and copolymer grades under different brand names.

What is POM material used for?

POM (polyoxymethylene) is used for precision mechanical parts requiring low friction, tight tolerances, and dimensional stability: gears, bushings, bearings, rollers, valve bodies, pump components, food processing parts, and electrical connectors. Its machinability — clean chips, tight tolerances, no coolant required — makes it the first-choice engineering plastic for CNC-machined precision parts.

Is acetal stronger than nylon?

Acetal has higher tensile modulus (stiffness) than nylon and far better dimensional stability because it absorbs less than 0.25% moisture versus 1.5% (PA12, equilibrium) to 8.5% (PA6, fully saturated) depending on nylon grade and humidity exposure. However, nylon typically has higher impact toughness. The correct comparison depends on the application: acetal wins for precision sliding fits; nylon wins for high-impact, high-temperature applications.

What temperature can acetal handle?

Acetal (POM) has a continuous service temperature of approximately 90–100°C (194–212°F) for unfilled grades. Short-term peak exposures up to 120°C are tolerable. Above 100°C continuous, POM begins to creep under load and loses significant stiffness. For applications above 120°C, consider PEEK (250°C continuous) or other high-performance polymers.

Does acetal absorb water?

Acetal absorbs very little moisture — typically less than 0.25% at 50% RH equilibrium versus 2.5–3% for PA6 nylon at the same conditions (or up to 8.5% when fully saturated by immersion). This low moisture absorption is the primary reason acetal maintains tight dimensional tolerances in humid environments. Precision bearing and gear applications where nylon would swell dimensionally are ideal acetal applications.

Can acetal be CNC machined?

Acetal (POM) is one of the most machinable engineering plastics. It produces clean, short chips at high speeds, requires no coolant for most operations, holds tight tolerances (±0.001 in readily achievable), and gives excellent surface finish with standard carbide tooling. Its predictable chip behavior makes it far easier to machine than most nylons or polycarbonate.

Is Delrin food safe?

Natural (white/ivory) Delrin and natural-grade acetal POM-H are compliant with FDA 21 CFR 177.2470 for food contact applications. Black acetal typically uses carbon black pigments that may not meet FDA requirements — always verify the specific grade with the material supplier. For confirmed FDA-grade acetal, specify "natural color, FDA-compliant grade" explicitly in your drawings.

Related Resources

Acetal vs. Nylon

Side-by-side engineering plastic comparison

CNC Machining Acetal

Speeds, feeds, tolerances, and DFM rules

Acetal Gear Design Guide

Module, PV limits, POM-on-steel pairing

Material Selection Guide

Full framework: metals, plastics, composites

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