POM / Delrin vs PET
POM (Delrin) and PET are both stiff, low-friction semi-crystalline engineering thermoplastics used for precision machined and molded parts. Delrin is prized for dimensional stability, fatigue resistance, and clean machining in tight-tolerance components. PET is a lower-cost alternative with good wear and chemical resistance, common in food-contact and moving parts. The right choice depends on tolerance precision, fatigue loading, and budget.
The verdict
Choose POM (Delrin) for precision parts needing the best dimensional stability, fatigue strength, and clean low-friction machining. Choose PET when you want good wear and chemical resistance at lower cost. Both are stiff and slide well; Delrin holds tolerances better while PET trims material cost.
Side-by-side data
| Property | POM / Delrin | PET |
|---|---|---|
| Category | Engineering Plastic | Engineering Plastic |
| Density (g/cm³) | 1.41 | 1.38 |
| Tensile strength (MPa) | 70 | 55 |
| Yield strength (MPa) | 65 | 50 |
| Elongation (%) | 40 | 70 |
| Hardness | R120 | R106 |
| Max service temp (°C) | 90 | 70 |
| Machinability | ●●●●● | ●●●●● |
| Corrosion resistance | ●●●●● | ●●●●● |
| Relative cost | ●●●●● | ●●●●● |
| Thermal cond. (W/m·K) | 0.31 | 0.24 |
| Typically used for | Precision low-friction machined parts | Bottles, fibers & food packaging |
Which should you choose?
Choose POM / Delrin when…
- Tight tolerances must hold — Delrin's low moisture absorption gives excellent dimensional stability
- Parts see cyclic or fatigue loading (gears, snap-fits, springs) where Delrin's fatigue resistance shines
- You machine precision components; Delrin rates 4.5/5 machinability versus PET at 3.5/5
- Slightly higher strength and stiffness help — tensile ~70 MPa vs PET's ~55 MPa (nominal)
- Continuous service can reach ~90 C versus PET's ~70 C in this dataset
- Low-friction, low-wear bushings, bearings, and rollers are the target
Choose PET when…
- Material cost matters — PET is ~1.5/5 cost versus Delrin at ~2.0/5
- You need good wear and chemical resistance in a stiff thermoplastic
- Parts are food-contact or packaging-adjacent, a traditional PET strength
- Tolerances are moderate and extreme dimensional precision is not required
- The part is injection molded or extruded rather than precision machined
- Higher elongation (~70% vs Delrin's ~40%) gives a bit more forgiveness before fracture
Key differences that matter
- Both are stiff, semi-crystalline, low-friction plastics good for wear and sliding parts
- Delrin machines more cleanly (4.5/5 vs 3.5/5), making it the precision-machining favorite
- Delrin's low moisture uptake gives superior dimensional stability for tight-tolerance parts
- Delrin outperforms in fatigue, favoring gears, snap-fits, and repeatedly flexed features
- PET is cheaper (~1.5/5 vs 2.0/5) with good chemical and wear resistance
- Delrin tolerates more heat here (~90 C vs ~70 C max service)
- PET shows higher elongation (~70% vs ~40%), giving slightly more strain tolerance
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Open the Material SelectorGet a Quote →Frequently asked questions
Is Delrin or PET better for precision machined parts?
Delrin. It machines very cleanly (4.5/5), produces excellent surface finish, and its low moisture absorption keeps parts dimensionally stable after machining. PET machines acceptably (3.5/5) but Delrin is the established choice for tight-tolerance bushings, gears, and instrument components where dimensional repeatability is critical.
Which material is cheaper?
PET is the lower-cost option, rated ~1.5/5 versus Delrin at ~2.0/5 in this dataset. The gap is modest but real, and PET still offers good wear and chemical resistance. For high-volume parts where extreme dimensional precision and fatigue performance are not required, PET can deliver similar function at lower material cost.
Which handles fatigue and repeated flexing better?
Delrin (POM). It is well known for fatigue endurance and resilience, which is why it dominates gears, snap-fit latches, and spring elements that cycle repeatedly. PET is stiff and stable but does not match Delrin's fatigue life, so for repeatedly loaded mechanical features Delrin is the safer engineering choice.
Can both be used for food-contact parts?
PET has a long track record in food packaging and food-contact applications. Specific Delrin (POM) grades are also available with food-contact compliance. For either material, you must confirm the exact grade carries the relevant FDA or EU food-contact certification — base resin family alone does not guarantee compliance.
Which tolerates higher temperatures?
Delrin, modestly. This dataset lists its continuous service near 90 C versus PET around 70 C. Neither is a high-temperature plastic, so for hot environments you would step up to PPS, PEEK, or similar. Between these two, Delrin gives a small thermal margin alongside its dimensional-stability advantage.
Property values are typical/nominal figures for early-stage guidance only and vary by temper, grade, supplier and heat treatment. Confirm critical specifications against a certified datasheet or with an mfgiq engineer before production.