Delrin for Your Engineering Projects
Choosing the right material is one of the biggest risks in product design. Delrin (POM homopolymer) is widely used for precision components, but engineers often struggle to know when it’s the best fit — and when another material will perform better. This post was written to cut through that uncertainty and provide practical design guidance.
Delrin is most valuable for parts that need high stiffness, excellent wear resistance, and tight tolerances while remaining cost-effective in moderate environments. It offers better dimensional stability and machinability than many plastics, but may fall short under high heat or aggressive chemicals.
Learn how Delrin compares to acetal copolymer, the tolerances it holds, its sliding load behavior, and common design mistakes to avoid.
Table of Contents
When should I consider Delrin for my engineering project?
Delrin is worth considering when your design needs a balance of stiffness, precision, and wear resistance that cheaper plastics can’t reliably deliver. It is often chosen as a substitute for metals when weight, machining cost, or corrosion resistance are concerns, yet tight tolerances and dimensional stability remain important.
Typical use cases include gears, sliding components, precision housings, and snap-fit designs — parts where low friction and consistent fit over time matter. Delrin can usually achieve ±0.05 mm tolerances on standard features, with ±0.01 mm possible on critical ones, making it more precise than many plastics. Its tensile strength (60–70 MPa) and low moisture uptake (<0.2%) also help maintain stability in assemblies.
However, Delrin should not be specified for continuous high-heat environments (above ~90–100 °C), or in contact with aggressive chemicals like strong acids and bases, as it can degrade prematurely. In those cases, alternatives such as PEEK, PTFE, or metals are better suited.
Design Takeaway: Consider Delrin when you need a machinable, dimensionally stable plastic that holds tight fits and performs reliably in moving or load-bearing parts. Avoid it in high-temperature or chemically harsh conditions, and use the following sections to evaluate its strength, tolerances, wear resistance, and cost in more detail.
How does Delrin compare to acetal copolymer?
Delrin (POM homopolymer) delivers higher stiffness and fatigue resistance, while acetal copolymer provides better chemical durability and stability in hot, wet conditions. The right choice depends less on headline strength numbers and more on how the part will actually be used.
Delrin typically achieves tensile strength of 65–70 MPa and has excellent fatigue endurance, which makes it well-suited for gears, bushings, and linkages that experience repeated loading. Its rigidity ensures close fits and reduced wear over long cycles. By contrast, acetal copolymer has slightly lower mechanical strength (~60 MPa), but absorbs less moisture and shows superior resistance to stress-cracking and hot-water attack, making it more reliable for fluidic housings, plumbing connectors, and medical components that see cleaning agents.
From a manufacturability standpoint, both machine well, but Delrin tends to cut cleaner, which helps when tight tolerances or polished surfaces are required. Copolymer’s advantage is dimensional stability on larger molded parts, where Delrin may exhibit slight centerline porosity or shrinkage.
Design Takeaway: Use Delrin when strength, stiffness, and fatigue life are the priority — especially in moving parts. Use copolymer when chemical resistance, hot-water stability, or large part consistency matter more. Choosing correctly avoids costly redesigns caused by cracking, warping, or premature wear.
Will Delrin provide the strength and stiffness my design needs?
Delrin is strong and stiff enough to replace nylon in precision housings, gears, and snap-fit parts, but it should not be treated as a substitute for aluminum in structural load paths. With tensile strength around 65 MPa and flexural modulus near 2,800 MPa, it offers a reliable balance of rigidity and machinability.
In practice, Delrin’s advantage over nylon is clear: it absorbs far less moisture (<0.2% vs nylon’s 2–3%), which means parts maintain their dimensions and tolerances over time. This makes it particularly attractive for audio gears, medical device housings, or aerospace spacers, where even small dimensional drift could cause assembly failures. Compared with metals, however, Delrin’s lower modulus limits its use in high-load or high-temperature parts. Above 90–100 °C continuous service, it begins to creep and lose stiffness, which can compromise critical fits.
Delrin’s toughness (elongation at break 25–40%) also helps snap-fit designs survive repeated use, but engineers should avoid over-relying on it for impact resistance. When the part must withstand structural bending or long-term load without deformation, aluminum or reinforced plastics remain the safer choice.
Design Takeaway: Delrin provides excellent stiffness and dimensional stability for medium-load, precision parts, but it is not a universal replacement for metals. Apply it where rigidity and stability matter most, and respect its thermal and load limitations to avoid premature failures.
Can Delrin hold the tolerances I specify?
Delrin can reliably hold ±0.05 mm for most features, and with stable fixturing and climate control, tolerances as tight as ±0.01 mm are achievable. For plastic machining, this is exceptional, but designers must be realistic about when such precision is justified.
Delrin’s low moisture absorption (<0.2%) makes it far more dimensionally stable than nylon, which often swells and throws off tolerances after machining. On a CNC mill, Delrin cuts cleanly, producing crisp edges without excessive burrs. For critical fits — such as gear bores, bearing seats, or precision housings — tolerances around ±0.01–0.02 mm are possible, though they may increase machining time and inspection cost. For non-critical dimensions, ±0.05 mm is sufficient and avoids unnecessary expense.
Thermal expansion is another factor: Delrin has a coefficient of linear expansion around 110 µm/m·°C, so tolerances specified without considering service temperature can still lead to dimensional drift. This matters most in assemblies exposed to heat cycles or variable environments.
Design Takeaway: Specify tight tolerances only on features that control function — such as fits, sealing surfaces, or gear engagement. Apply ISO 2768-m or looser tolerances on cosmetic or non-critical features. This keeps machining cost and inspection requirements under control while ensuring Delrin’s stability is fully leveraged.
How well does Delrin perform in sliding or wear applications?
Delrin performs exceptionally well in sliding and wear conditions thanks to its low coefficient of friction (~0.2) and excellent fatigue resistance. It is often chosen over nylon for bushings, gears, and linkages that must run smoothly without external lubrication.
The homopolymer’s crystalline structure provides superior wear life compared to many plastics. In dry running applications, Delrin’s surface resists galling and maintains dimensional stability, while nylon tends to swell with moisture and introduce drag. Designers often rely on Delrin for gears in audio devices, actuator components in automotive assemblies, and bearing surfaces in medical devices, where consistent movement over thousands of cycles is required.
That said, Delrin is not invincible. Continuous sliding at high loads or elevated temperatures (above 90–100 °C) can accelerate creep and reduce wear life. Filled grades (with PTFE or glass) are sometimes used to extend performance, but they can also make machining more difficult. In environments where abrasive particles are present, Delrin may wear faster than UHMW-PE or reinforced nylons.
Design Takeaway: Use Delrin confidently for medium-load sliding parts, precision gears, and bushings, especially where moisture control and dimensional stability matter. For very high-load, high-heat, or abrasive environments, consider reinforced alternatives or metals. Balancing these limits avoids premature wear and ensures long-term reliability.
Will Delrin absorb moisture and change dimensions over time?
Delrin absorbs less than 0.2% moisture, compared to 2–3% for nylon, so dimensional change is almost negligible in most environments. For designers, this means close-fitting assemblies and gears stay in spec without the swelling problems common to other plastics.
To put it in scale: a nylon housing stored in humid air might grow 0.3 mm over 100 mm length, while Delrin would shift only about 0.02 mm under the same conditions. This stability makes Delrin a reliable option for gears, bushings, medical housings, or snap-fit designs, where repeatable fit is critical.
The bigger concern is thermal expansion, not moisture. With a coefficient of linear expansion of about 110 µm/m·°C, Delrin will move more under temperature swings than from humidity. For example, a 50 mm gear could expand 0.15 mm going from 20 °C to 50 °C — something to account for in assemblies.
Design Takeaway: Use Delrin confidently when you need dimensionally stable parts that won’t swell like nylon. Allow for slight movement in hot environments, but don’t overspec tolerances for moisture concerns. If your design involves full immersion or sterilization cycles, validate stability under those specific conditions.
Can Delrin handle temperature and chemical exposure?
Delrin performs well up to about 85 °C, but begins to creep above 90–100 °C in continuous service. Chemically, it resists oils, fuels, and most solvents, but it cannot withstand strong acids, bases, or oxidizers without degrading.
As a rule of thumb: if your part will see temperatures higher than boiling water or cleaners stronger than diluted bleach, Delrin may not be the right choice. In automotive fuel systems or pump housings, it holds up well against hydrocarbons and alcohols. In medical applications, however, it is not suitable for steam sterilization (autoclaving), where repeated cycles will cause distortion.
Short-term heat spikes to ~120 °C can be tolerated for light loads, but creep and distortion become risks at sustained high temperatures. For harsher environments, materials like PEEK, PTFE, or reinforced copolymers are more reliable options.
Design Takeaway: Use Delrin with confidence for oil- and fuel-contact parts at moderate temperatures, but avoid it in continuous high-heat or chemically aggressive environments. If your application involves hot water sterilization, concentrated cleaners, or long-term thermal stress, specify a higher-grade polymer to prevent failures.
What surface finishes or coatings are recommended for Delrin?
Most Delrin parts do not require coatings, and a standard machined finish of Ra 3.2 µm is acceptable for functional components. With polishing, Ra 0.8–1.6 µm can be achieved for sealing or cosmetic surfaces.
For functional parts such as gears, bushings, and spacers, the natural low-friction surface is often sufficient. If the part is visible to end users, specify polishing or light bead blasting to improve appearance. Delrin machines cleanly, so you can achieve a uniform matte or smooth finish without secondary treatments.
Coatings are rarely successful because Delrin’s surface resists bonding. Painting or plating requires primers, etching, or plasma treatment, which adds cost and reliability risk. If you want color coding, branding, or graphics, molded-in pigment or pad printing works better than surface coatings. For wear-heavy applications, a filled Delrin grade (PTFE or glass) is the right solution, since surface coatings won’t last under friction.
Design Takeaway: If the part is functional, no finish is needed. If cosmetic, call for polishing or bead blasting. If you need wear resistance, choose a filled grade rather than trying to coat Delrin. For branding, specify molded-in color or printing instead of painting.
Is Delrin cost-effective compared to metals and plastics?
Delrin is more cost-effective than aluminum for precision plastic parts but costs more than commodity plastics like ABS or polypropylene. The value comes from its balance of machinability, dimensional stability, and reduced finishing requirements.
In practice, replacing a small aluminum gear with Delrin can cut machining time by 20–30% and eliminate secondary treatments like anodizing or corrosion protection. Procurement teams often find this lowers both unit price and lead time. Compared to nylon, Delrin reduces rejects by holding ±0.05 mm tolerances consistently, avoiding swelling-related assembly issues.
However, Delrin is not always the cheapest choice. For non-critical housings or low-load parts, ABS or polypropylene offer lower raw material cost. For high-heat or structural parts, aluminum or PEEK may justify their higher price because they avoid failures that Delrin cannot withstand.
Rule of thumb cost hierarchy (lowest → highest): ABS/PP < Delrin < Aluminum < PEEK.
Design Takeaway: Use Delrin when precision, stability, and reduced finishing costs outweigh slightly higher material price. Avoid it for purely cosmetic or non-critical parts where cheaper plastics work, or for heavy-duty parts where metals or high-performance polymers are justified.
What design mistakes should I avoid with Delrin parts?
The biggest mistakes with Delrin come from treating it like metal or nylon instead of recognizing its unique limits. Over-specifying tolerances, ignoring thermal expansion, or relying on coatings are common errors that add cost or reduce reliability.
One frequent pitfall is calling for unnecessarily tight tolerances across an entire drawing. While Delrin can achieve ±0.01 mm, this level of precision should be reserved for critical features like bores or sealing edges. Specifying it on every surface increases machining time and inspection costs without improving function.
Another mistake is overlooking thermal expansion. With a coefficient of ~110 µm/m·°C, parts that fit at room temperature may bind or loosen in service if the environment fluctuates. Designers should avoid very long unsupported spans or ensure assemblies can accommodate slight dimensional shifts.
Surface treatments also trip up many developers. Painting or plating Delrin is unreliable without special preparation, and coatings often fail under wear. For cosmetic or branding needs, specify molded color, pad printing, or polishing instead.
Finally, don’t assume Delrin can replace metals in high-heat or heavy-load parts. Above 90–100 °C, creep becomes a risk, and structural loads may exceed its modulus.
Design Takeaway: Treat Delrin as a high-performance plastic, not a drop-in metal substitute. Use tight tolerances sparingly, account for expansion, and avoid coating-based solutions. Following these rules keeps designs reliable and cost-effective.
Conclusion
Delrin delivers reliable stiffness, wear resistance, and dimensional stability when applied correctly. It should not be over-specified like metal or under-designed like nylon. If your project demands precision plastics, consult with a machining partner who can guide tolerance choices and application limits — avoiding costly mistakes while keeping performance on target.
Frequently Asked Questions
Not ideal. While Delrin is tough, polypropylene and polyethylene perform far better in thin hinge sections. If a hinge must be used in Delrin, design it thicker and expect shorter cycle life. For reliable long-term hinges, avoid Delrin.
Yes, Delrin’s toughness (elongation at break 25–40%) makes it well-suited for snap-fits. It resists cracking better than brittle plastics and holds shape over repeated flexing. Avoid overly sharp corners — adding small radii reduces stress and extends part life.
Bonding Delrin is difficult due to its low surface energy. Standard adhesives fail unless surfaces are plasma- or chemically treated. For assemblies, designers typically use mechanical fastening (screws, inserts, clips) instead of adhesives.
Yes, food-grade Delrin grades exist and are FDA/NSF compliant. They are commonly used in conveyor rollers, pumps, and kitchen equipment. Always confirm the grade’s certification with your supplier — not every Delrin grade is food-approved.
Not without stabilization. Standard Delrin will chalk and lose toughness in direct sunlight. If outdoor use is unavoidable, choose UV-stabilized grades or design protective covers. For long-term outdoor parts, consider copolymer acetals with UV additives.
Delrin threads and snap features work for occasional use, but they can wear over many cycles. For frequent assembly, specify metal threaded inserts or bushings to protect the polymer and keep tolerances stable.
