Acetal vs. Polycarbonate: Engineering Comparison (2026)

The Core Trade-Off: Transparency vs. Chemical Resistance

Before you choose between acetal and polycarbonate, identify your dominant failure mode — that single factor usually makes the decision obvious. Polycarbonate wins on transparency (optical clarity) and impact toughness. Acetal wins on chemical resistance, wear resistance, dimensional stability, and machinability. If you need to see through the part or absorb major impacts, reach for PC. If the part will see fluid exposure, sliding contact, or needs tight CNC tolerances, reach for acetal. The decision is usually clear once you identify the dominant failure mode.

Section 1 of 5

Full Property Comparison

When you evaluate acetal against polycarbonate, these property numbers drive your material selection for CNC parts. Key mechanical, thermal, and physical properties side-by-side.

Property	Acetal (POM-H)	Polycarbonate (PC)	Winner
Tensile strength	69 MPa (10,000 psi)	62–72 MPa (9,000–10,500 psi)	Tie
Flexural modulus	2.8 GPa (400 ksi)	2.3 GPa (330 ksi)	Acetal
Compressive strength	124 MPa (18,000 psi)	86 MPa (12,500 psi)	Acetal
Izod impact (notched)	75–120 J/m (1.4–2.2 ft·lb/in)	850–900 J/m (16 ft·lb/in)	Polycarbonate
Hardness (Rockwell M)	M 80–94	M 62–70	Acetal
Coefficient of friction (vs. steel)	0.20–0.35	0.35–0.45	Acetal
Wear resistance	Excellent — self-lubricating	Poor — scores rapidly	Acetal
Max continuous service temp	90–100°C (194–212°F)	115–125°C (240–257°F)	Polycarbonate
CTE (thermal expansion)	110 µm/m·°C	65–70 µm/m·°C	Polycarbonate
Water absorption (24 hr)	0.22%	0.15%	Polycarbonate
Transparency	Opaque	Optically clear	Polycarbonate
Density	1.41–1.42 g/cc	1.20 g/cc	PC (lighter)
Chemical resistance	Excellent (broad)	Poor — ESC risk	Acetal
UV resistance (standard)	Moderate	Poor — yellows	Tie (both need UV grade)
Cost (stock material)	Moderate	Moderate–Low	Polycarbonate

Section 2 of 5

Where Polycarbonate Wins: Impact and Clarity

If your part must survive sudden impacts or transmit light, polycarbonate is the only viable choice between these two materials. Two properties where PC clearly outperforms acetal — backed by 10–15× higher Izod impact and optical transparency — and when they matter.

Impact Toughness: PC Has a 10–15× Advantage

Polycarbonate's notched Izod impact strength of 850–900 J/m is one of the highest of any rigid thermoplastic. Acetal lands at 75–120 J/m. This difference is dramatic in applications subject to sudden impact loads: protective covers, safety glasses, structural brackets that must survive drops, and housings that need to absorb tool strikes or equipment collisions without fracturing.

Applications where PC wins on impact:

•Machine guarding and safety shields
•Enclosure lids and access panels
•Handheld tool housings
•Bracket arms subject to accidental impact

Optical Clarity: PC Is the Only Choice When Transparency Is Required

Standard polycarbonate has 85–90% light transmission — comparable to glass. Acetal is entirely opaque. There is no transparent acetal. If the part requires the user to see through it, observe flow, monitor a level, or pass light, polycarbonate (or acrylic) must be used. Acetal is fundamentally opaque; this is a material property that cannot be engineered around.

Applications where PC wins on clarity:

•Sight glasses and flow windows
•Machine guarding where visibility matters
•Light pipes and diffusers
•Fluid level indicators

Pro Tip: Acrylic vs. PC for Transparency

If the transparent part does not need high impact resistance, acrylic (PMMA) is often a better choice than PC: lower cost, better scratch resistance, and no solvent-stress-cracking concern. Use PC over acrylic only when the part must survive significant impact loads.

Section 3 of 5

Chemical Resistance: Acetal vs. PC

If your part contacts solvents, cutting oils, or cleaning agents, this section determines whether polycarbonate is even an option for you. Environmental stress cracking (ESC) is polycarbonate's primary failure mode in industrial environments.

Acetal Chemical Resistance Profile

Acetal resists most non-oxidizing acids, aliphatic hydrocarbons, alcohols, mild bases, and many solvents. Key exceptions: strong oxidizing acids (concentrated sulfuric, nitric), halogens, and strong bases at elevated temperatures.

Fuels (gasoline, diesel)Excellent

Hydraulic fluid (mineral oil)Excellent

Alcohols (IPA, methanol)Excellent

Cutting oils and coolantsExcellent

Mild acids (dilute)Good

Strong oxidizing acidsPoor

Polycarbonate ESC Risk: The Most Common Failure Mode

Environmental stress cracking (ESC) is the dominant failure mode for polycarbonate in industrial service. Under residual stress (from machining, assembly, or molding), PC crack propagates rapidly when exposed to compatible chemicals.

Organic solvents (acetone, MEK)Severe ESC

Mold releases and lubricantsESC risk

Cutting oils and coolantsModerate risk

Fuels (gasoline)ESC risk

Bleach and disinfectantsESC risk

Dilute acids and basesModerate

CNC Acetal and Polycarbonate — Precision Machined Parts

MakerStage machines both acetal (POM-H, POM-C) and polycarbonate to tight tolerances. Our team reviews DFM on every order — including material selection guidance if your application is at the acetal/PC decision boundary. Free DFM review with every RFQ.

Get a CNC Plastic Parts Quote

Section 4 of 5

Machinability: Acetal vs. Polycarbonate

If your drawing calls for ±0.003 in. or tighter, machinability differences between these materials directly affect your part cost and lead time. Both plastics machine well, but acetal is the preferred choice for tight-tolerance, high-volume work.

Acetal (POM)

Chip typeShort, clean chips — good chip evacuation

Achievable tolerance±0.002 in (±0.05 mm) standard

Surface finishRa 32–63 µin as-machined without secondary ops

Tool wearLow — machines without rapid tool wear

Coolant needDry or light air blast sufficient

Drill performanceExcellent — sharp drill, no peck needed

ThreadingTap at standard speeds; thread rolling preferred for high strength

Key advantagePredictable, dimensionally stable under machining forces

Polycarbonate (PC)

Chip typeStringy chips — require chip breaking attention

Achievable tolerance±0.003–0.005 in — material compliance and residual stress complicate tight work

Surface finishGood, but surface stresses from machining can cause later ESC

Tool wearLow — similar to acetal

Coolant needDry or water mist; avoid solvent-based cutting fluids (ESC risk)

Drill performanceGood — peck drilling recommended for deep holes

ThreadingTap with sharp taps; avoid over-torque which causes cracking

Key concernResidual machining stress + subsequent chemical exposure = ESC failure

Section 5 of 5

Application Decision Matrix

Choose the right plastic based on your application's dominant failure mode and functional requirements.

Choose Acetal (POM/Delrin) when:

Sliding contact, bearing, bushing, or wear application
Fluid handling — valves, fittings, pump components
Chemical environment with oils, fuels, or solvents
Precision machined part requiring ±0.002 in or tighter
Food contact or FDA-compliant application (natural grade)
Self-lubricating performance required
Gear, rack, or cam application

Choose Polycarbonate (PC) when:

Transparency or optical clarity is a hard requirement
Severe impact resistance needed (guarding, safety shields)
Higher continuous service temperature than acetal (up to 125°C)
Lighter weight is important (PC is ~15% lighter than acetal)
No chemical exposure or fully controlled clean environment
Thin-walled structural housing with impact requirement

Do not use Polycarbonate when:

Any sliding contact or wear application
Exposure to solvents, cutting oils, fuels, or most cleaning agents
Precision tight-tolerance CNC work (±0.002 in or better)
Parts will be assembled with adhesives containing solvents
Long-term outdoor UV exposure without UV-stabilized grade

Do not use Acetal when:

Transparency is required — acetal is always opaque
Very high impact loads that could fracture the part
Strong oxidizing acid or bleach environments
Operating above 90°C continuous (consider PEEK or PSU)
Autoclave sterilization required (use PEEK)

Frequently Asked Questions

Is acetal or polycarbonate stronger?

It depends on how you define "stronger." Polycarbonate has significantly higher impact strength — roughly 10–15× higher Izod impact than acetal (POM). For applications that must absorb sudden impact without fracturing, PC wins. But acetal has higher tensile and compressive strength for static loading, better hardness (Rockwell M 80–94 vs. PC's M 62–70), and superior wear resistance. For load-bearing structural parts that don't experience shock loads, acetal is often the stronger choice.

Can polycarbonate replace acetal in a bushing application?

No. Polycarbonate is a poor choice for bearings and bushings. PC has a much higher coefficient of friction (approximately 0.40 vs. acetal's 0.20–0.35 against steel), no self-lubricating properties, and much lower wear resistance. Polycarbonate will score, gall, and wear rapidly in sliding-contact applications. Acetal is specifically recommended for self-lubricating bushings, wear pads, and guide rails. For any tribological application, use acetal (or filled acetal), not PC.

Why does polycarbonate crack when exposed to chemicals?

Polycarbonate is susceptible to environmental stress cracking (ESC) in the presence of many chemicals — particularly organic solvents, mold releases, cutting oils, acetone, certain fuels, and even some cleaning agents. Under molded-in or applied stress, these chemicals rapidly propagate micro-cracks. Acetal (POM) is significantly more resistant to ESC and tolerates a broader range of chemicals without cracking. This is why acetal is preferred in fluid handling components and environments where chemical exposure is likely.

Which is better for machining: acetal or polycarbonate?

Both machine well, but acetal (POM) is generally preferred for tight-tolerance, high-volume machining. Acetal produces better chip control (short chips vs. PC's stringy chips), takes tighter tolerances more reliably (±0.002 in vs. PC's ±0.003–0.005 in), has lower thermal expansion, and doesn't require the same care against surface stress. Polycarbonate is more prone to surface stress from machining that can later cause cracking under chemical exposure. For precision parts requiring ±0.002 in or tighter, acetal is the easier plastic to qualify.

Is polycarbonate or acetal better for outdoor applications?

Neither is excellent outdoors without UV stabilization, but they fail differently. Standard polycarbonate yellows and embrittles under UV exposure — UV-stabilized PC grades significantly extend outdoor life. Standard acetal retains mechanical properties better under UV than PC, but also degrades gradually. Both should have UV-stabilized grades specified for long-term outdoor exposure. If the part must be transparent (light covers, windows), UV-stabilized PC is the only practical choice since acetal is opaque.