Acetal Filled Grades: PTFE, Glass, Carbon (2026)

Q: What is Delrin AF?

Delrin AF is Celanese's trade name for PTFE-filled acetal homopolymer (POM-H + approximately 18–20% PTFE fiber). The PTFE filler reduces the dry coefficient of friction from 0.20–0.35 (unfilled) to approximately 0.05–0.15 vs steel, and significantly extends bearing and bushing service life. It is the standard self-lubricating bearing grade when unfilled POM produces unacceptable wear rates in high-duty-cycle applications.

Q: Does PTFE-filled acetal machine well?

PTFE-filled acetal (AF grade) machines similarly to unfilled POM — same speeds, feeds, and tooling. The PTFE filler actually provides additional lubrication at the cutting edge, which can improve tool life slightly. The main difference: PTFE-filled POM produces a fine, powdery dust rather than clean chips in some operations. Adequate chip and dust evacuation is important, and PTFE dust should not be breathed.

Q: When should I use glass-filled acetal instead of unfilled?

Use glass-filled acetal (typically 25–30% short glass fiber) when you need significantly higher stiffness and strength at elevated temperature, or when creep under sustained load at 60–80°C is a concern. Glass-filled POM has 2× the tensile modulus of unfilled, much better elevated-temperature stiffness retention, and improved creep resistance. Trade-off: higher coefficient of friction and abrasive action on mating metal surfaces — do not run glass-filled acetal against soft metals.

Q: Is carbon-filled acetal worth the cost?

Carbon-fiber-filled acetal (10–20% chopped carbon fiber) provides the highest stiffness and lowest CTE of all POM grades, plus good electrical conductivity (ESD dissipative at carbon loading levels). It is appropriate for precision structural brackets requiring maximum stiffness at minimal weight, ESD-sensitive environments, and tribological applications where the self-lubricating carbon fiber improves wear at high load. Machining is harder — carbon fiber is abrasive and increases tool wear versus unfilled POM.

Q: What is a PV limit?

PV stands for Pressure × Velocity — a combined parameter used to characterize bearing and sliding applications. Pressure (P) is the bearing load divided by projected area (MPa or psi); Velocity (V) is the sliding speed (m/s or ft/min). The PV limit is the maximum product of P and V at which the material can sustain continuous operation without thermal failure at the bearing interface. Exceeding the PV limit causes the bearing surface to overheat, soften, and fail rapidly.

Start With Unfilled POM. Upgrade Only When PV Limits or Wear Rates Demand It.

Unfilled acetal handles the majority of gear, bushing, and cam applications without modification. Specialty filled grades cost more, can be harder to source, and in the case of glass-filled POM, introduce mating-surface wear concerns. This guide helps you identify the specific conditions where a filled grade delivers a measurable performance advantage — not just a theoretical one.

Section 1 of 5

Unfilled Acetal: The Baseline

Before you upgrade to a filled grade, you need to know what unfilled POM already delivers — it handles most gear, bushing, and cam applications without modification. Know the baseline before evaluating upgrades. Unfilled POM is already a high-performance bearing material for most applications.

0.20–0.35

Dry CoF vs steel

Lower than most engineering plastics

~0.10 MPa·m/s

PV limit (continuous)

Suitable for most low-duty gear and cam applications

6–12 mg/1,000 cycles

Taber wear rate

Good wear resistance for dry sliding at low PV

When Unfilled POM Is Sufficient

For gears, bushings, and cams running at PV below 0.08 MPa·m/s with dry contact and ambient temperature, unfilled POM-H or POM-C is the correct specification. Adding a filled grade adds cost and sourcing complexity for no measurable benefit in these conditions.

Section 2 of 5

PTFE-Filled Acetal (AF Grade)

If your bearing or bushing application exceeds unfilled POM's dry PV limit of ~0.10 MPa·m/s, PTFE-filled acetal is the first filled grade to evaluate. The self-lubricating bearing grade. PTFE fiber content (typically 18–20%) reduces dry friction dramatically and extends wear life in high-duty-cycle applications.

PTFE-Filled Acetal Properties (Delrin AF / equivalent)

PTFE content18–20% fiber

Dry CoF vs steel0.05–0.15

PV limit (continuous)~0.20 MPa·m/s

Tensile strength~55 MPa (slightly lower than unfilled)

Tensile modulus~2,500 MPa (lower than unfilled)

MachinabilityExcellent — PTFE lubricates cutting edge

FDA complianceNatural grade available; verify specific batch

When to Specify PTFE-Filled Acetal

Use it when:

Application PV exceeds 0.08 MPa·m/s continuous
Part runs at medium duty cycle (>30 minutes/hour)
Mating metal surface is soft (aluminum, brass) and unfilled POM wear rate is too high
Application requires the lowest possible dry friction coefficient
Bearing surface temperature risk is moderate — PTFE filler helps dissipate heat

Do not use when:

Part is subject to high structural load (PTFE filler reduces tensile strength ~20%)
Application requires food-contact compliance — verify PTFE grade FDA status first
Cost is critical — AF grade is 2–3× unfilled POM price

Section 3 of 5

Glass-Filled Acetal (25–30% GF)

If your part needs higher stiffness or better creep resistance at elevated temperature, glass-filled acetal doubles the modulus — but you must design around mating-surface abrasion. The structural upgrade grade. Glass fiber reinforcement doubles stiffness and significantly improves elevated-temperature performance — at the cost of increased friction and mating-surface abrasion.

GF25 Acetal Properties (vs. unfilled baseline)

Glass fiber content25–30% short glass fiber

Tensile strength (UTS)~110 MPa (+59% vs unfilled)

Tensile modulus~6,200 MPa (2× unfilled)

Dry CoF vs steel0.35–0.50 (worse than unfilled)

Elevated-temp stiffness retentionSignificantly better to 120°C

Creep resistanceGreatly improved vs unfilled POM

MachinabilityGood — glass fiber increases tool wear vs unfilled

Critical Warning: Mating Surface Abrasion

Glass fiber in POM is abrasive to softer mating materials. Do not run glass-filled acetal against:

Aluminum alloys (6061, 7075)
Brass or bronze
Soft steel (< HRC 30)
Other plastics as mating gear or bushing

Safe mating materials: hardened steel (HRC 45+), hard chrome, stainless steel 17-4 PH.

Section 4 of 5

Carbon-Filled Acetal (CF Grade)

If your application requires ESD dissipation or the lowest possible thermal expansion from a plastic part, carbon-filled acetal is the premium option to evaluate. The precision structural and ESD (Electrostatic Discharge) grade. Chopped carbon fiber provides maximum stiffness, lowest CTE, and electrical conductivity — for ESD-sensitive environments and high-precision structural plastic parts.

CF20 Acetal Properties (vs. unfilled)

Carbon fiber content15–20% chopped fiber

Tensile modulus~7,500 MPa (2.4× unfilled)

CTE~50 µm/m·°C (vs 110 unfilled)

Dry CoF vs steel0.15–0.25 (self-lubricating)

Surface resistivity10³–10⁶ Ω/sq (ESD dissipative)

MachinabilityGood — CF is abrasive; use fresh carbide tooling

When CF Acetal Earns Its Place

ESD-sensitive environments (semiconductor handling, electronics assembly jigs)
High-precision structural brackets where minimal thermal expansion is required
Bearing applications combining load and moderate sliding velocity where self-lubricating carbon fiber improves PV limit
Wafer handling fixtures, PCB handling trays, and tooling where static charge dissipation is critical

CNC Machining in All Acetal Grades

MakerStage machines unfilled acetal (POM-H, POM-C), PTFE-filled (AF grade), and glass-filled acetal for CNC precision parts. Free DFM review on every order — we'll confirm the right grade for your application before quoting.

Get a CNC Acetal Quote with Free DFM Review

Section 5 of 5

Full Grade Comparison Table

Use this table to compare all four grades side by side when making your material selection — it covers every property that affects your design and sourcing decisions. All grades at 23°C, dry conditions unless noted. Filled grade properties vary by specific filler loading — values shown for typical commercial grades.

Property	Unfilled POM	PTFE-Filled AF	Glass-Filled 25%	Carbon-Filled 20%
Tensile Strength	69 MPa (10.0 ksi)	~55 MPa (~8.0 ksi)	~110 MPa (~16.0 ksi)	~80 MPa (~11.6 ksi)
Tensile Modulus	3,100 MPa	~2,500 MPa	~6,200 MPa	~7,500 MPa
Dry CoF vs steel	0.20–0.35	0.05–0.15	0.35–0.50	0.15–0.25
PV limit (cont.)	~0.10 MPa·m/s	~0.20 MPa·m/s	~0.06 MPa·m/s	~0.15 MPa·m/s
Wear rate (Taber)	6–12 mg/1k	2–5 mg/1k	3–6 mg/1k	3–7 mg/1k
Elevated-temp stiffness	Good	Good	Excellent	Very Good
ESD dissipative	No (insulator)	No (insulator)	No	Yes (10³–10⁶ Ω/sq)
Machinability	Excellent	Excellent	Good	Good (abrasive)
Mating surface abrasion	Low	Very Low	High — avoid soft metals	Moderate
Cost vs unfilled	Baseline	2–3× unfilled	1.5–2× unfilled	3–5× unfilled
FDA natural grade	Yes	Check grade	Generally No	No

Frequently Asked Questions

What is Delrin AF?

Delrin AF is Celanese's trade name for PTFE-filled acetal homopolymer (POM-H + approximately 18–20% PTFE fiber). The PTFE filler reduces the dry coefficient of friction from 0.20–0.35 (unfilled) to approximately 0.05–0.15 vs steel, and significantly extends bearing and bushing service life. It is the standard self-lubricating bearing grade when unfilled POM produces unacceptable wear rates in high-duty-cycle applications.

Does PTFE-filled acetal machine well?

PTFE-filled acetal (AF grade) machines similarly to unfilled POM — same speeds, feeds, and tooling. The PTFE filler actually provides additional lubrication at the cutting edge, which can improve tool life slightly. The main difference: PTFE-filled POM produces a fine, powdery dust rather than clean chips in some operations. Adequate chip and dust evacuation is important, and PTFE dust should not be breathed.

When should I use glass-filled acetal instead of unfilled?

Use glass-filled acetal (typically 25–30% short glass fiber) when you need significantly higher stiffness and strength at elevated temperature, or when creep under sustained load at 60–80°C is a concern. Glass-filled POM has 2× the tensile modulus of unfilled, much better elevated-temperature stiffness retention, and improved creep resistance. Trade-off: higher coefficient of friction and abrasive action on mating metal surfaces — do not run glass-filled acetal against soft metals.

Is carbon-filled acetal worth the cost?

Carbon-fiber-filled acetal (10–20% chopped carbon fiber) provides the highest stiffness and lowest CTE of all POM grades, plus good electrical conductivity (ESD dissipative at carbon loading levels). It is appropriate for precision structural brackets requiring maximum stiffness at minimal weight, ESD-sensitive environments, and tribological applications where the self-lubricating carbon fiber improves wear at high load. Machining is harder — carbon fiber is abrasive and increases tool wear versus unfilled POM.

What is a PV limit?

PV stands for Pressure × Velocity — a combined parameter used to characterize bearing and sliding applications. Pressure (P) is the bearing load divided by projected area (MPa or psi); Velocity (V) is the sliding speed (m/s or ft/min). The PV limit is the maximum product of P and V at which the material can sustain continuous operation without thermal failure at the bearing interface. Exceeding the PV limit causes the bearing surface to overheat, soften, and fail rapidly.