Delrin vs Acetal: Which High-Performance Plastic Wins?
Tensile data verified against MatWeb.com database & manufacturer datasheets · Last updated July 2026
Published: 2026-07-21
Which Material Should You Choose?Choose Delrin Homopolymer if:High-stiffness precision components requiring maximum mechanical propertiesgears, springs, clips, and structural parts where higher tensile strength, stiffness, and hardness provide...
Which Material Should You Choose?
Choose Delrin Homopolymer if:
- High-stiffness precision components requiring maximum mechanical properties
- gears, springs, clips, and structural parts where higher tensile strength, stiffness, and hardness provide measurable performance advantage
Choose Acetal Copolymer if:
- Applications involving hot water, steam, or aggressive chemical environments
- plumbing fittings, water handling, food processing, and parts requiring better long-term thermal stability and reduced centerline porosity
Price Comparison
Delrin Homopolymer: $5-10/kg vs Acetal Copolymer: $5-10/kg · Prices vary by grade and quantity
Delrin homopolymer (POM-H) and Acetal copolymer (POM-C) are both polyoxymethylene engineering plastics, but the difference in their polymerization — homopolymer vs copolymer — produces distinct performance profiles that matter in demanding applications. Delrin is DuPont's trade name for POM-H (made from formaldehyde); Acetal copolymer (POM-C, made from trioxane with a small amount of comonomer) is produced by Celanese (Celcon), BASF (Ultraform), and others. While often treated as interchangeable, the choice between them becomes critical in three scenarios: thick-section parts, hot water applications, and maximum-load precision components.
When to choose Delrin Homopolymer (POM-H): Delrin's fully homopolymer chain provides 10-15% higher tensile strength (70 vs 62 MPa), higher flexural modulus (2900 vs 2600 MPa), and greater surface hardness (M94 vs M90 Rockwell). These advantages make Delrin the preferred choice for precision gears requiring maximum tooth stiffness, snap-fit clips requiring high spring-back force, and structural components operating at maximum load. Delrin's higher melting point (175 vs 165°C) provides a marginal advantage in short-term high-temperature excursions. Delrin also has better fatigue resistance in cyclically loaded applications — it is often specified for living hinges and snap domes that must survive millions of cycles. However, Delrin has a critical weakness: centerline porosity. In extruded rods and thick injection-molded sections (>12mm), Delrin can develop a porous centerline due to gas evolution during polymerization. This porosity is invisible on the part surface but creates leak paths in valve bodies, weak points in structural parts, and cosmetic defects in machined surfaces. For thick-section parts, Acetal copolymer is always the safer choice.
When to choose Acetal Copolymer (POM-C): The copolymerization with a small amount of comonomer (typically 2-5% of an ethylene oxide or dioxolane unit) breaks up the regularity of the polymer chain. This provides three critical advantages: (1) No centerline porosity — POM-C can be extruded and molded in thick sections without the gas evolution problem that plagues Delrin; (2) Better hot water and steam resistance — the copolymer chain is more resistant to the acid-catalyzed depolymerization that destroys homopolymer in hot water; while POM-C is still not recommended for continuous hot water above 60°C, it survives short-term hot water exposure far better than POM-H; (3) Superior long-term thermal stability — POM-C retains its properties better over years of service at elevated temperatures, making it preferred for under-hood automotive components and continuous-use applications. POM-C also has slightly better chemical resistance to alkalis and stronger resistance to oxidative degradation.
Processing considerations: Both materials process well on standard injection molding equipment. POM-H processes at melt temperatures of 190-220°C; POM-C at 180-210°C. Both require corrosion-resistant screws and barrels (POM decomposes to formaldehyde, which is acidic). POM-C has a slightly wider processing window and is more forgiving of processing variations. For machined parts from extruded rod, POM-C is strongly preferred due to absence of centerline porosity — machined Delrin parts often reveal porous centers that compromise seal integrity and mechanical strength. For food contact and medical applications, both materials have FDA-compliant grades; POM-C's better hot water resistance gives it an edge in cleaning and sterilization scenarios.
Comparison at a Glance
| Material A | Delrin Homopolymer POM (POM-H) |
|---|---|
| Material B | Acetal Copolymer POM (POM-C) |
| Polymer Type | POM-H: Semicrystalline (Tm 175°C) | POM-C: Semicrystalline (Tm 165°C) |
| Continuous Temp A | 100 °C |
| Continuous Temp B | 100 °C |
| Tensile Strength A | 70 MPa |
| Tensile Strength B | 62 MPa |
| Cost Relative | Delrin homopolymer costs approximately 10-15% more than acetal copolymer due to DuPont brand premium and more demanding polymerization process |
| Best For A | High-stiffness precision components requiring maximum mechanical properties — gears, springs, clips, and structural parts where higher tensile strength, stiffness, and hardness provide measurable performance advantage |
| Best For B | Applications involving hot water, steam, or aggressive chemical environments — plumbing fittings, water handling, food processing, and parts requiring better long-term thermal stability and reduced centerline porosity |
| Key Differentiator | POM-H (Delrin): 10-15% higher tensile strength and stiffness, higher melting point (175 vs 165°C), better creep resistance, but susceptible to centerline porosity in thick sections and poor hot water resistance. POM-C (Copolymer): superior thermal and chemical stability, no centerline porosity, better hot water resistance, more consistent properties in thick sections, but 10-15% lower mechanical properties. |
Frequently Asked Questions
Are Delrin and Acetal the same material?
No, but they are closely related. Both are polyoxymethylene (POM), but Delrin is specifically homopolymer POM (POM-H) made by DuPont, while Acetal typically refers to copolymer POM (POM-C) made by Celanese (Celcon), BASF (Ultraform), and others. The difference is in polymerization: homopolymer has a perfectly regular chain of -CH2-O- repeat units, while copolymer includes 2-5% of a different comonomer that breaks the chain regularity. This gives Delrin 10-15% higher mechanical properties but makes it susceptible to centerline porosity and hot water degradation. Acetal copolymer has slightly lower mechanical properties but better thermal/chemical stability. In many applications they are interchangeable, but in thick sections, hot water service, or maximum-load applications, the choice matters.
What is centerline porosity and why does it affect Delrin but not Acetal copolymer?
During homopolymer POM polymerization, residual formaldehyde gas and water vapor can become trapped in the center of thick extruded or molded sections as the material cools. This creates a porous, spongy core that is invisible on the part surface but dramatically reduces mechanical strength and creates leak paths. The copolymerization process in POM-C releases fewer volatiles during solidification, eliminating this problem entirely. If you machine a part from Delrin rod stock and expose the center, you may see a porous, discolored core. For valve bodies, seal seats, or any part where leak-tightness matters, always specify Acetal copolymer. For thin-section parts (<6mm) where porosity doesn't develop, Delrin is safe to use.
Which POM grade is better for gears?
For precision instrument gears requiring maximum tooth stiffness and minimal deformation under load, Delrin homopolymer is preferred — its 10-15% higher modulus and hardness translate directly to better gear performance (less tooth deflection, better positioning accuracy, higher torque capacity). For power transmission gears in thicker sections, or gears that may see hot water cleaning (food processing, appliance), Acetal copolymer is preferred due to absence of porosity and better thermal stability. For thin-section instrument gears (<6mm wall), Delrin is excellent. For thick-section gears (>12mm), Acetal copolymer is the safer choice to avoid porosity-related tooth failure.
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References & Industry Standards
- ASTM International. Standard Specifications for Engineering Plastics & Thermoplastics. astm.org
- UL Prospector. Plastics & Elastomers Material Database. ulprospector.com
- MatWeb. Material Property Data for Engineering Thermoplastics. matweb.com
- ISO 1043. Plastics — Symbols and Abbreviated Terms. iso.org