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Here's a question that trips up even seasoned engineers: Is Delrin just acetal with better marketing? The short answer: yes and no. The long answer could save you thousands in material costs and machining headaches. When you're spec'ing parts for CNC machining, injection molding, or rapid prototyping, picking the wrong grade means wasted time, scrapped parts, and a frustrated production team.
This guide clears up the Delrin vs acetal confusion once and for all. Here's what we'll cover:
● What is acetal (and what is Delrin, really)
● Key property differences between grades of Delrin and grades of acetal
● Best applications for CNC machining, injection molding, and rapid prototyping
● How to choose the right material for your project
At TEAM MFG, we machine and mold both materials daily for clients across 73 countries. We've seen what works and what doesn't.
Acetal is the common name for polyoxymethylene (POM), a semi-crystalline engineering thermoplastic known for its high strength, low friction, and exceptional dimensional stability. You might also hear it called polyacetal or polyformaldehyde. Same material, different names.
What makes acetal stand out from commodity plastics like PVC or polyethylene? Its molecular structure. The repeating –CH₂–O– backbone creates a highly crystalline material that holds tight tolerances, resists wear, and performs consistently under stress.
The material exists in two distinct forms:
● Homopolymer Acetal (POM-H): Made from pure, anhydrous formaldehyde. Higher crystallinity means better mechanical properties, but with trade-offs.
● Copolymer Acetal (POM-C): Contains about 1-1.5% ethylene oxide in its structure. Slightly lower strength, but improved chemical and thermal stability.
Homopolymer acetals display significantly higher tensile strength than copolymer acetals. We're talking roughly 15% better performance in hardness, stiffness, and compressive strength. POM-H can also bear about 10% higher loads before exhibiting creep.
So why would anyone choose a copolymer? Chemical resistance. Copolymer acetal exhibits good resistance against chemicals in the pH range of 4 to 13, while homopolymer is limited to pH 4-9. For wet environments or hot water applications, POM-C wins.
Property | Value Range |
Density | 1.41–1.42 g/cm³ |
Tensile Strength | 60–70 MPa |
Moisture Absorption | ~0.2% (very low) |
Continuous Use Temp (POM-H) | Up to 90°C in air |
Continuous Use Temp (POM-C) | Up to 100°C in air |
Coefficient of Friction | ~0.18 (self-lubricating) |
Different applications demand different performance characteristics. Manufacturers have responded with specialized grades:
● Standard unfilled grades: General-purpose machining and molding
● Glass-filled grades: Enhanced stiffness and strength (typically 20-25% glass fiber)
● PTFE-filled grades: Superior lubricity for high-wear applications
● Food-grade acetal: FDA, USDA, and NSF compliant for food contact
● Metal-detectable grades: Used in food processing to catch contamination
Homopolymers' more basic structure gives it higher physical properties, making it the correct choice for applications like gears and structural supports. But if you need to machine large cross-sections or tubes, copolymer is your only option. POM-H simply can't be manufactured in those forms.
Acetal shows up in nearly every industry that requires precision parts:
● Automotive: Fuel system components, door locks, gears, bushings
● Medical: Surgical handles, insulin pens, inhalers
● Consumer electronics: Housing materials, switches, moving parts
● Food processing: Conveyor components, valves, packaging machinery
● Industrial: Bearings, pump parts, wear strips, manifolds
The material machines beautifully, producing clean chips with minimal tool wear. That's one reason it's a favorite for CNC machining when tight tolerances matter.
Delrin is a brand name. Nothing more, nothing less.
The Du Pont Company offered the first commercial acetal homopolymer under the trademark Delrin acetal resin in January 1960. Over 60 years later, the name has become so synonymous with acetal homopolymer that engineers use "Delrin" and "POM-H" interchangeably. It's like calling all adhesive bandages "Band-Aids" or all facial tissues "Kleenex."
Delrin specifically refers to acetal homopolymer (POM-H), not the copolymer version. When someone says "Delrin," they're talking about the premium, higher-crystallinity version of acetal plastic.
What makes Delrin different from generic acetal copolymer comes down to molecular structure. Homopolymers have a uniform backbone made with repeating CH2O units, which makes it possible to create larger crystalline blocks than other POMs.
Those larger crystalline blocks translate to real-world performance advantages:
● Higher tensile and flexural strength
● Better stiffness and rigidity
● Superior creep resistance under load
● Improved fatigue endurance
● Excellent "spring back" or shape memory
Delrin acetal homopolymer resin is one of the most crystalline engineering thermoplastics available. That crystallinity is both its greatest strength and its limitation (more on that shortly).
Delrin isn't a single material. It's a product family with dozens of formulations. Delrin plastic is available in many grades, including 100, 500, 900, and 1700. The grades refer to their melt viscosity, with 100 the most viscous and 1700 the most fluid.
Here's a breakdown of the most common grades:
Grade | Viscosity | Best For |
Delrin 100 | Highest | Maximum toughness, impact resistance, fatigue endurance |
Delrin 500 | Medium | General-purpose injection molding, balanced properties |
Delrin 900 | Low | Thin-wall parts, complex geometries, fast cycling |
Delrin 1700 | Lowest | Multi-cavity molds, long flow paths, intricate details |
The resins in the Delrin 100 series are distinguished by their high molecular weight relative to other acetal grades. Higher molecular weight means better mechanical properties, but slower flow during molding. Lower viscosity grades fill molds faster but sacrifice some strength.
Beyond the standard viscosity grades, DuPont developed specialty formulations for specific applications:
● Delrin AF (100 & 500): Contains 13-20% PTFE fibers for reduced friction and improved wear resistance. With its superior low-friction and low-wear characteristics, Delrin AF 500 is often applied in bearings, gears, and bushings where durability is essential.
● Delrin 570: Contains 20% glass reinforcement, offering greater stiffness and creep resistance. Commonly chosen for automotive and structural components under constant load.
● Delrin UV grades (127UV, 527UV, 927UV): Chemically stabilized for outdoor use where UV exposure exceeds one year.
● Delrin AF DE588: A specialized 20% PTFE grade approved by the U.S. Navy for submarine components and demanding military applications.
No material is perfect. Delrin's Achilles' heel is centerline porosity.
Due to the manufacturing process, large-diameter cross-sections may have pronounced centerline porosity. During cooling, gas escapes from the center of extruded stock shapes, creating microscopic voids along the centerline.
What does this mean for your parts?
● Potential mechanical weakness at the core
● Risk of leakage in pressurized fluid applications
● Bacterial growth concerns for certain foods and medical uses
If you're machining parts from rod stock, buy oversized material and machine away the porous center. Or consider copolymer acetal, which exhibits significantly less centerline porosity.
Delrin's combination of strength, stiffness, and dimensional stability makes it ideal for:
● Gears and drive components: The self-lubricating surface reduces friction without external lubricants
● Bearings and bushings: Performs 4-to-1 better than nylon in wet environments
● Fuel system parts: Excellent resistance to gasoline, diesel, and automotive fluids
● Fasteners and clips: Spring-back properties allow repeated deflection without permanent deformation
● Electrical insulators: High dielectric strength with low moisture absorption
Typical applications for injection-molded POM include high-performance engineering components like gear wheels, ski bindings, fasteners, and lock systems.
On paper, Delrin (POM-H) and acetal copolymer (POM-C) look almost identical. In most applications, Delrin and acetal copolymer can be interchanged as their material properties are within approximately 10% of each other.
But that 10% difference? It can make or break your project.
Property | Delrin (POM-H) | Acetal Copolymer (POM-C) | Winner |
Tensile Strength | ~11,000 psi | ~9,500 psi | Delrin |
Flexural Strength | ~13,000 psi | ~12,000 psi | Delrin |
Stiffness | Higher | Lower | Delrin |
Hardness | 86 Shore D | 85 Shore D | Tie |
Chemical Resistance (pH range) | 4–9 | 4–13 | Copolymer |
Hot Water Resistance | Up to 60°C | Up to 85°C | Copolymer |
Centerline Porosity | Pronounced | Minimal | Copolymer |
Thermal Expansion | Lower | Higher | Delrin |
Continuous Service Temp | ~90°C | ~100°C | Copolymer |
Cost | 10–15% higher | Lower | Copolymer |
● Mechanical performance. The strength and stiffness of unfilled homopolymer acetal (Delrin) is approximately 15% greater than those of the copolymer acetals. That gap widens even further when you compare high-molecular-weight grades like Delrin 100P against standard copolymers.
● Fatigue endurance. If your part experiences repeated loading and unloading cycles, Delrin is the clear choice. Homopolymer POM (e.g., injection molded Delrin) has greater fatigue strength than copolymer POM. Gears, springs, and snap-fit assemblies benefit from this property.
● Creep resistance. Under constant load, Delrin holds its shape better over time. This matters for structural components, bearings under sustained pressure, and precision assemblies that can't afford dimensional drift.
● Spring-back memory. Delrin's higher crystallinity gives it superior "elastic memory." Parts return to their original shape after deflection, making it ideal for clips, latches, and living hinges.
● Chemical and hydrolysis resistance. Copolymer acetals exhibit substantially greater resistance to hydrolysis (degradation by hot water) and better dimensional stability. If your part will see steam, hot water, or caustic cleaners, POM-C is the safer bet.
● Centerline porosity. This is a big one. Acetal experiences less centerline porosity than Delrin, which is very prone to centerline porosity. For thick cross-sections, pressurized fluid applications, or anywhere structural integrity at the core matters, the copolymer delivers more consistent properties throughout.
● Processability. If your part design has thin walls, tight internal corners, or intricate features, Acetal tends to mold more easily and with less internal stress. Copolymer fills molds better, shrinks more predictably, and produces fewer cosmetic defects.
● Food and medical applications. The lower porosity of the copolymer means less potential for bacterial growth. Many food-grade and medical-grade acetals are copolymer formulations.
Both material families offer specialty grades tailored to specific needs:
Grade Type | Delrin Options | Copolymer Options |
PTFE-filled (low friction) | Delrin AF 100, AF 500 | Acetron GP + PTFE |
Glass-reinforced | Delrin 570, 525GR | Celcon GC-25A |
UV-stabilized | Delrin 127UV, 527UV | Multiple options |
Static dissipative | ESD Delrin | ESD Copolymer |
Super-tough | Delrin 100ST, 500ST | Impact-modified grades |
Glass-filled acetal can see significant increases in strength and stiffness because the copolymer structure bonds well with the glass fibers. If you need reinforcement, copolymer often outperforms homopolymer in this regard.
Still not sure which to pick? Use this quick guide:
Choose Delrin when:
● Maximum mechanical strength is non-negotiable
● Parts experience cyclic loading or fatigue
● You need the lowest possible friction coefficient
● Dimensional precision under load is critical
● The application stays dry and avoids harsh chemicals
Choose Acetal Copolymer when:
● Hot water or steam exposure is expected
● Chemical resistance matters (especially to bases)
● You're machining thick cross-sections from rod stock
● Food contact or medical compliance is required
● Budget constraints favor lower material costs
● Complex mold geometries need forgiving flow characteristics
Choosing between Delrin and acetal is only half the equation. The manufacturing process you select shapes which material performs best, and vice versa.
Both materials machine like a dream. Delrin is a popular engineering thermoplastic for CNC machining, both because of its material properties and its machinability. You get clean chips, minimal tool wear, and the ability to hold tight tolerances.
Best practices for CNC machining acetal:
● Use sharp cutting tools. For Delrin CNC milling, it is recommended to use sharp cutting edges to facilitate continuous chip formation. Dull tools generate heat and can cause gumming.
● Go fast, feed slow. High cutting speeds with low feed rates produce the best surface finish and dimensional accuracy.
● Mind the heat. Delrin has a relatively low melting point (~175°C). Low melting point necessitates controlled tool speeds to avoid gumming. Use coolant at high speeds or take lighter passes.
● Single-flute end mills work best. Delrin milling requires single-fluted mills to prevent heat formation and low chip clearance.
● Account for centerline porosity. When machining Delrin rod stock, buy oversized material and machine away the porous center for critical parts.
Machining Parameter | Recommended Value |
Typical Tolerance | ±0.005" (±0.127mm) |
Cutting Speed | 200–500 ft/min |
Coolant | Optional (recommended at high speeds) |
Tool Material | HSS or carbide |
When to choose each material for CNC:
● Delrin: Precision gears, bearings, bushings, and structural components where mechanical strength matters
● Acetal copolymer: Fluid-handling parts, thick-wall components, and applications requiring consistent properties throughout the cross-section
This is where material selection gets interesting. Both materials mold well, but their behavior differs significantly.
The shrinkage challenge. POM is prone to shrinkage rates of 2 to 3.5%. That's considerably higher than amorphous plastics like ABS (0.5%) or polycarbonate (0.6%). This homopolymer POM variant has higher shrinkage rates than copolymer acetals.
What does high shrinkage mean for your mold design?
● Cavities must be oversized to compensate
● Uniform wall thickness becomes critical
● Gate location affects dimensional consistency
● Cooling must be carefully controlled
Delrin injection molding considerations:
● Higher crystallinity means more shrinkage and potential warpage
● Narrower processing window requires tighter control
● Most shrinkage occurs while the part is still within the mold during the cooling stage, but a small amount of shrinkage still occurs after ejection, especially for Delrin.
● Better suited for parts with simple geometries and consistent wall thickness
Acetal copolymer injection molding advantages:
● Copolymers have better thermal stability, chemical resistance and processibility.
● Wider processing temperature range forgives minor variations
● Acetal fills molds better, shrinks less inconsistently, and is more forgiving during cooling.
● Better choice for complex geometries with thin walls or intricate features
Molding Parameter | Delrin (POM-H) | Acetal Copolymer (POM-C) |
Melt Temp | 200–220°C | 190–210°C |
Mold Temp | 80–100°C | 60–90°C |
Shrinkage Rate | 2.0–3.5% | 1.8–2.5% |
Processing Window | Narrow | Wide |
Variations in mold surface temperature and mold injection pressure can cause shrinkage in test bars made from one specific grade, ranging from 1.8 to 5.0%. Run samples before committing to production tooling.
When speed matters more than volume, rapid prototyping lets you validate designs before investing in production tooling.
● CNC prototyping remains the gold standard for acetal parts. You get production-grade material properties in your prototype, which means functional testing actually tells you something useful. Turnaround times of 1–5 days are common for simple geometries.
● 3D printing with POM is possible but comes with trade-offs. 3D printing Delrin offers geometrical flexibility and is suitable for a very wide range of prototyping applications, but its limitations include poor print bed adhesion, possible delamination, and a limited temperature range.
If you need a functional prototype that behaves like the final injection-molded part, CNC machining beats 3D printing for acetal materials.
Rapid tooling for injection molding bridges the gap between prototyping and production. Aluminum molds can produce hundreds to thousands of parts in actual production-grade material, letting you validate both design and manufacturing process before cutting steel.
Application | Best Process | Recommended Material |
Functional prototype (1–10 parts) | CNC machining | Delrin or copolymer based on end-use |
Design validation (10–100 parts) | CNC or rapid tooling | Match production material |
Low volume (100–1,000 parts) | Rapid tooling or low-volume molding | Copolymer (easier processing) |
Medium volume (1,000–10,000 parts) | Injection molding | Application-dependent |
High volume (10,000+ parts) | Injection molding | Application-dependent |
At TEAM MFG, we support all three manufacturing paths: CNC machining, injection molding, and rapid prototyping. Our engineering team can help you select the right material and the right process based on your volume requirements, timeline, and performance needs. With over 15,000 completed projects across 73 countries, we've seen what works in real-world production.
You've made it this far. You understand the differences between Delrin and acetal copolymer. You know which manufacturing processes suit each material. Now comes the hard part: making the actual decision.
In some applications, Acetal may be better suited for long-term heat resistance. In others, where parts must withstand repeated loading, Delrin often proves more stable. The problem is, these differences aren't always obvious in the datasheet.
Let's fix that.
Before you spec a material, answer these five questions. They'll guide you to the right choice faster than any comparison table.
Environment dictates material more than any other factor.
Environment | Best Choice | Why |
Dry, room temperature | Either works | Properties are similar enough |
Hot water or steam | Copolymer | Superior hydrolysis resistance |
Outdoor/UV exposure | Neither (or UV-stabilized grade) | Both degrade in sunlight |
Chemical exposure (acids/bases) | Copolymer | Wider pH tolerance (4–13 vs. 4–9) |
High humidity | Copolymer | Lower moisture absorption |
Submerged in water | Copolymer | Consistent properties, less porosity |
Static loads and cyclic loads demand different materials.
● Static loads (constant pressure): Delrin's superior creep resistance keeps parts from deforming over time
● Cyclic loads (repeated stress): For the highest fatigue endurance, select Delrin 100. For example, in gear tests, Delrin 100 exhibits approximately 40% higher fatigue endurance.
● Impact loads: Delrin 100ST or impact-modified copolymer grades
● Light-duty or intermittent loads: Copolymer works fine and costs less
Tight tolerances require dimensional stability. Both materials offer excellent stability, but with caveats:
● Delrin: Lower thermal expansion, better under load, but higher mold shrinkage and post-mold shrinkage
● Copolymer: More predictable shrinkage, less centerline porosity, better for thick cross-sections
Delrin's higher crystallinity means it may shrink more after machining or molding. For ultra-tight tolerances, consider annealing Delrin parts to stabilize dimensions before final machining.
Geometry influences both material selection and manufacturing process.
Geometry Feature | Recommendation |
Thin walls (<1.5mm) | Copolymer (better mold flow, less warpage) |
Thick cross-sections (>25mm) | Copolymer (less centerline porosity) |
Snap-fits and living hinges | Delrin (better spring-back memory) |
Complex internal features | Copolymer (more forgiving during molding) |
Gears with fine teeth | Delrin (higher strength, better wear) |
5. What's the total cost of ownership?
Material cost is only part of the equation. Rather than focusing only on price-per-kilo or price-per-part, consider this question instead: What's the total cost of ownership if the part fails or underperforms?
Consider these hidden costs:
● Scrap rate: Copolymer's wider processing window often means fewer rejected parts
● Secondary operations: Delrin's better machinability may reduce finishing time
● Warranty claims: Choosing the wrong material leads to field failures
● Oversizing: If you choose a copolymer where Delrin would work, you may need thicker walls to match the strength
Once you've chosen Delrin or copolymer, you still need to pick the right grade.
For Delrin:
If You Need... | Choose This Grade |
Maximum toughness and fatigue resistance | Delrin 100 |
Balanced flow and properties | Delrin 500 |
Thin walls or complex geometries | Delrin 900 or 1700 |
Low friction and wear | Delrin AF (PTFE-filled) |
High stiffness and creep resistance | Delrin 570 (glass-filled) |
Outdoor UV exposure | Delrin 127UV, 527UV |
For Acetal Copolymer:
If You Need... | Choose This Grade |
General purpose | Standard unfilled copolymer |
Enhanced stiffness | Glass-filled copolymer |
Low friction | PTFE-filled copolymer |
Food contact compliance | FDA/NSF-compliant grades |
Static dissipation | ESD copolymer |
Sometimes acetal isn't the answer at all. Consider alternatives when:
● Temperatures exceed 120°C continuously: Look at PEEK, PPS, or PEI
● UV exposure is unavoidable: Consider ASA or UV-stabilized nylon
● Strong acids or oxidizers are present: PTFE or PVDF handles aggressive chemicals better
● Flame retardancy is required: Acetal burns readily; consider PC, PBT, or flame-retardant nylon
● Transparency is needed: Acetal is opaque; switch to polycarbonate or acrylic
Before finalizing your material selection, verify:
● [ ] Operating temperature range stays within material limits
● [ ] Chemical compatibility confirmed for all exposure scenarios
● [ ] Mechanical loads (static, cyclic, impact) matched to material strength
● [ ] Dimensional stability requirements achievable with the chosen material
● [ ] Manufacturing process (CNC, injection molding, 3D printing) compatible with the material
● [ ] Regulatory compliance (FDA, NSF, UL) confirmed if required
● [ ] Cost analysis includes tooling, scrap rate, and potential warranty exposure
● [ ] Prototype testing planned to validate real-world performance
Material selection isn't something you should guess at. The difference between a successful product launch and a costly recall often comes down to getting this decision right the first time.
The Delrin vs acetal debate doesn't have a universal winner. It has the right answer for your specific project. Delrin delivers when mechanical performance and fatigue resistance matter most. Acetal copolymer wins when chemical exposure, thick cross-sections, or processing ease take priority. Now you have the framework to choose confidently.
Key Takeaways:
● Delrin is a brand name for acetal homopolymer (POM-H), not a separate material
● Delrin offers ~15% higher strength and stiffness than acetal copolymer
● Acetal copolymer provides better chemical resistance (pH 4–13 vs 4–9) and hot water performance
● Delrin's centerline porosity makes the copolymer better for thick cross-sections and fluid applications
● Both materials machine beautifully; the copolymer molds more forgivingly
● Environment, mechanical loads, geometry, and total cost should drive your material decision
Whether you're prototyping a precision gear in Delrin or scaling production of fluid-handling components in acetal copolymer, TEAM MFG brings 12+ years of hands-on experience with both materials.
Our engineering team helps you select the right grade, optimize your design for manufacturing, and deliver quality parts from prototype through mass production. Request a quote today, and let's turn your next project into another success story.
