POM: Properties, Uses & Cost Guide
Tensile data verified against MatWeb.com database & manufacturer datasheets · Last updated July 2026
Published: 2026-06-02
Polyoxymethylene (POM, acetal) is the preferred material for precision mechanical components requiring low friction, high stiffness, and excellent dimensional stability. Two grades exist: homopolymer (Delrin, -CH2O-) with slightly higher...
Polyoxymethylene (POM, acetal) is the preferred material for precision mechanical components requiring low friction, high stiffness, and excellent dimensional stability. Two grades exist: homopolymer (Delrin, -CH2O-) with slightly higher crystallinity and mechanical strength, and copolymer (Celcon, Hostaform) with better thermal stability and chemical resistance. POM's 1.8-2.5% mold shrinkage is among the highest for engineering thermoplastics — this must be compensated in tool design.
Critical processing warning: POM degrades exothermically above 230°C, releasing formaldehyde gas. Overheated POM can cause a rapid pressure spike in the barrel due to formaldehyde gas generation. Never shut down a barrel containing POM — purge with HDPE or a commercial purge compound first. The characteristic pungent odor of formaldehyde at the mold is the primary warning sign of overheating. Processing window: melt temperature 190-210°C, mold temperature 80-100°C for optimal crystallinity.
Recommended Applications
POM is commonly specified for:
⚠ Not Recommended For
POM is not recommended for:
- Strong acid environments (sulfuric, nitric — POM hydrolyzes rapidly below pH 4)
- UV-exposed outdoor applications without carbon black loading (UV degrades rapidly)
- Continuous service above 100°C (use PPS or PEEK for high-temp structural instead)
Selection & Application Guide
POM (acetal/Delrin) is the premium choice for precision mechanical components requiring tight tolerances, low friction, and excellent dimensional stability. Choose POM over nylon when moisture absorption and dimensional stability are critical — POM absorbs 10× less moisture than nylon. Choose POM over PBT when fatigue resistance and creep resistance are needed. POM's low friction and wear resistance make it the standard for gears, bearings, and sliding mechanisms.
Real-World Applications
POM's low friction (μ=0.1-0.3), excellent fatigue resistance, and dimensional stability make it the standard material for small precision gears in office equipment, automotive actuators, and consumer products.
POM's resistance to gasoline, ethanol blends, and diesel fuel, combined with low permeability, makes it standard for fuel sender units, fuel caps, and valve bodies.
POM's wear resistance and low friction suit it for conveyor chain links, wear strips, and guide rails in packaging and material handling systems.
POM's precision moldability, low friction, and biocompatibility (USP Class VI) make it ideal for metered-dose inhaler valves and dose counters.
Processing & Cost Considerations
Manufacturing Tips
- POM processes easily at 185-215°C melt temperature with mold temperatures of 80-100°C. It has a narrow processing window — avoid temperatures above 220°C as POM decomposes with formaldehyde release. Ensure adequate ventilation.
- POM is highly crystalline and shrinks significantly (1.8-2.5%). Mold design must account for this shrinkage, especially for precision gear teeth and bearing surfaces. Post-molding shrinkage continues for 24-48 hours.
- Homopolymer acetal (Delrin) has higher tensile strength and stiffness; copolymer acetal (Duracon/Celcon) has better chemical resistance to hot water and strong bases. Choose homopolymer for maximum mechanical performance; copolymer for chemical exposure.
POM costs $5-10/kg — slightly more than nylon but offering superior dimensional stability and lower friction. The total cost advantage of POM over nylon often comes from eliminating secondary operations (no moisture-conditioning needed, tighter as-molded tolerances). POM is not a high-temperature polymer (max 100°C continuous); for higher temperatures, consider PPS or PEEK.
Technical Properties
| Density | 1.41 g/cm³ |
|---|---|
| Tensile Strength | 70 MPa |
| Melting Point | 175 °C |
| Shrinkage Rate | 1.8-2.5% |
| Flexural Modulus | 2.8 GPa |
| Hdt | 110 °C at 1.82 MPa |
Engineering Tool: Shrinkage & Cost Estimator
Calculate part weight, mold cavity dimensions accounting for shrinkage, and material cost — all locally in your browser.
Equivalents & Cross-References
| Equivalent / Alternate | Action |
|---|---|
| Delrin 500P | |
| Hostaform C9021 | |
| Tenac C |
Frequently Asked Questions
What is the difference between POM homopolymer and copolymer?
Homopolymer (Delrin) has ~5% higher tensile strength and stiffness. Copolymer (Celcon/Hostaform) has better thermal stability and chemical resistance, especially to hot water and bases. For most applications, copolymer is preferred unless the extra 5% mechanical performance is critical.
Can POM be overmolded with TPE?
No. POM's low surface energy and high crystallinity prevent adhesion to TPEs and most adhesives. Surface treatment (plasma, corona, or chemical etching) is required. If overmolding is needed, consider PA66 or PBT as the rigid substrate — these bond well with TPEs.
What is the difference between homopolymer and copolymer POM?
Homopolymer (Delrin) has higher tensile strength (70 MPa vs 61 MPa), stiffness, and fatigue endurance. Copolymer (Duracon/Celcon) has better thermal stability, chemical resistance to hot water and alkalis, and less formaldehyde outgassing during processing. For most mechanical applications, homopolymer is preferred; for hot water or chemical exposure, copolymer is safer.
Can POM be used for drinking water applications?
Copolymer POM grades are certified to NSF/ANSI 61 for potable water contact. Homopolymer POM generally does not have this certification due to residual formaldehyde. For plumbing components in contact with drinking water, always specify NSF-certified copolymer POM.
Is POM suitable for snap-fit assembly?
Yes, POM is excellent for snap-fits due to its high fatigue endurance and elastic recovery. However, POM has low elongation at break (15-25% for homopolymer), so snap-fit designs must avoid excessive strain during assembly. The allowed strain for POM snap-fits is typically 4-6% for unreinforced grades.
Why does POM release formaldehyde during processing?
POM is a polyoxymethylene that can depolymerize (unzip) from chain ends when overheated, releasing formaldehyde gas. This is more pronounced in homopolymer than copolymer. The copolymer's C-C bond in the backbone interrupts the unzipping reaction. Always process POM within the recommended temperature range and ensure adequate ventilation.
Can POM be bonded with adhesives?
POM is notoriously difficult to bond due to its low surface energy and chemical inertness. Mechanical fastening and snap-fits are preferred. When adhesive bonding is necessary, surface treatment (plasma, corona, or chemical etching) plus cyanoacrylate or two-part epoxy provides moderate bond strength. Welded joints (ultrasonic, hot plate) are stronger than adhesive bonds.
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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