Overview
Delrin and Nylon 6/6 are the two most common engineering plastics in CNC machine shops. They look similar. They feel similar. But they behave very differently when exposed to moisture, heat and friction.
Delrin is a brand name for acetal homopolymer (POM-H). It is made by Celanese (formerly DuPont). Nylon 6/6 is a polyamide. Both are white or off-white thermoplastics used for gears, bushings, rollers, guides and structural brackets.
The biggest difference between them comes down to one thing: water. Nylon absorbs moisture and swells. Delrin does not. That single fact drives most of the decision-making between these two materials.
Properties Comparison Table
All values are for standard, unfilled grades at room temperature and 50% relative humidity.
| Property | Delrin (POM) | Nylon 6/6 |
|---|---|---|
| Tensile Strength | 10 ksi | 12 ksi |
| Flexural Modulus | 410 ksi | 400 ksi |
| Density | 0.051 lb/in³ | 0.041 lb/in³ |
| Moisture Absorption (24 hr) | 0.22% | 1.2% |
| Moisture Absorption (saturation) | 0.9% | 2.5% |
| Coefficient of Friction (vs steel) | 0.20 | 0.30–0.40 |
| Max Continuous Temperature | 180 °F | 220 °F |
| Dimensional Stability | Excellent | Poor (swells with humidity) |
| Impact Resistance | Good | Very Good |
| Chemical Resistance | Good (weak to strong acids) | Good (weak to strong acids and oxidizers) |
| FDA Food Contact | Yes | Yes |
| Machinability | Excellent | Good |
| Relative Cost | 1x (baseline) | 0.8–0.9x |
Moisture Absorption and Dimensional Stability
This is the single most important difference between these two materials. It affects tolerances, fit and long-term performance.
Nylon Absorbs Water
Nylon 6/6 absorbs up to 2.5% moisture by weight when fully saturated. In a humid factory or outdoors, a Nylon part can swell by 0.6 to 1.2% in each direction. On a 4-inch part, that is up to 0.048 inches of growth. That is enough to turn a slip fit into a press fit, jam a sliding mechanism, or blow a tolerance.
Nylon parts machined in a dry shop will grow after they leave. If your part needs to hold tight tolerances in a humid environment, Nylon is risky.
Delrin Stays Stable
Delrin absorbs only 0.22% moisture in 24 hours and maxes out at about 0.9% when fully saturated. On that same 4-inch part, growth is less than 0.004 inches. That is 12 times less than Nylon. For parts that need to hold ±0.002 inches or tighter, Delrin is the safer bet.
If your part has tight fits, sliding surfaces, or lives in a humid or wet environment, choose Delrin. If moisture is not a concern and you need more impact resistance, Nylon works fine.
Friction and Wear
Delrin has a coefficient of friction of about 0.20 against steel. Nylon 6/6 is higher, around 0.30 to 0.40. That makes Delrin the better choice for:
- Gears: Lower friction means less heat buildup and longer gear life. Delrin gears run quieter too.
- Bearings and bushings: Delrin bushings slide smoother with less stick-slip behavior.
- Conveyor guides: Delrin guide rails cause less drag on belts and chains.
- Rollers: Delrin rollers turn more freely and wear more evenly.
Nylon does have one friction advantage: it handles heavy loads better. Under high contact pressure, Nylon's toughness helps it resist gouging and surface damage. For heavy-duty bushings in construction or agricultural equipment, Nylon 6/6 can outlast Delrin.
Machinability
Both materials machine well on standard CNC mills and lathes. But Delrin is easier overall.
Delrin Machining
- Cuts clean with sharp, well-defined chips.
- Does not gum up or melt onto the cutting tool.
- Holds tight tolerances (±0.001 inches is achievable on small features).
- Excellent surface finish straight off the machine (8–16 Ra microinches).
- Can be machined dry, though light air blast helps clear chips.
Nylon Machining
- Slightly more prone to gumming at high spindle speeds.
- Can melt if the tool is dull or feeds are too slow.
- Chips tend to be stringy and long. Keep chip-breaking feeds.
- Tolerances are harder to hold because the material flexes more under cutting forces.
- Surface finish is good but not quite as crisp as Delrin (16–32 Ra microinches typical).
For tight-tolerance parts with fine features, Delrin is the machinist's first choice. For simple shapes where tolerance is not critical, either material works.
Chemical Resistance
Both materials resist most common chemicals, but they have different weak spots.
| Chemical | Delrin | Nylon 6/6 |
|---|---|---|
| Gasoline and oils | Excellent | Excellent |
| Weak acids | Poor | Poor |
| Strong acids (sulfuric, hydrochloric) | Not recommended | Not recommended |
| Weak bases | Good | Good |
| Strong bases (sodium hydroxide) | Good | Fair |
| Alcohols | Good | Excellent |
| Hot water (above 140 °F) | Fair (can hydrolyze) | Fair (absorbs more water) |
For fuel system parts, hydraulic components and oil-exposed applications, both materials work well. For anything involving strong acids, neither is a good choice. Consider PEEK or Polycarbonate instead.
Cost Comparison
Nylon 6/6 rod stock is about 10 to 20% cheaper per pound than Delrin. For a 2-inch diameter, 12-inch long rod:
- Delrin: $25–$35
- Nylon 6/6: $20–$28
But material cost is only part of the picture. Delrin machines faster and holds tolerances better, so you may need fewer inspection passes and less rework. For tight-tolerance parts, Delrin often costs less to machine even though the stock is more expensive.
For simple parts with loose tolerances (bushings, spacers, non-critical guides), Nylon saves money. For precision parts (gears, valve seats, instrument components), Delrin usually wins on total cost.
Applications
Best Applications for Delrin
- Precision gears and gear trains
- Bearings and bushings for linear motion systems
- Conveyor guides and chain wear strips
- Valve seats and plumbing fittings
- Electrical insulator blocks
- Food processing equipment (FDA compliant)
- Precision fixtures and alignment pins
- Semiconductor wafer handling components
Best Applications for Nylon 6/6
- Structural brackets that need impact resistance
- Cable ties, clamps and snap-fit features
- Heavy-duty bushings under high compressive loads
- Wear pads for construction and mining equipment
- Pulleys and sheaves
- Parts that see temperatures above 180 °F
- Automotive under-hood components
- Packaging machinery components
How to Choose: A Simple Decision Guide
Answer these five questions to pick the right material:
- Will the part be in a humid or wet environment? If yes, choose Delrin. Nylon will swell and lose accuracy.
- Does the part need tight tolerances (±0.002 inches or better)? If yes, choose Delrin. Its dimensional stability is far better.
- Is the part a gear, bearing, or sliding surface? If yes, choose Delrin. Lower friction and better wear properties.
- Will the part see temperatures above 180 °F? If yes, choose Nylon 6/6. It handles higher temperatures.
- Does the part need to survive heavy impacts? If yes, choose Nylon 6/6. It absorbs more energy before breaking.
If you are still not sure, upload your CAD file and our engineers will recommend the best plastic for your application.
For a broader look at all CNC-compatible materials, check our CNC materials handbook.
Frequently Asked Questions
Is Delrin stronger than Nylon?
Nylon 6/6 has slightly higher tensile strength (12 ksi vs 10 ksi). But Delrin has better stiffness and dimensional stability. Delrin holds tighter tolerances while Nylon absorbs more energy before breaking.
Does Nylon absorb water?
Yes. Nylon 6/6 absorbs up to 2.5% moisture. This causes swelling of 0.6 to 1.2%. Delrin absorbs only 0.22% moisture and barely changes size at all.
Which has lower friction, Delrin or Nylon?
Delrin. Its coefficient of friction against steel is about 0.20, while Nylon 6/6 is 0.30 to 0.40. Delrin is better for gears, bearings and sliding parts.
Can you CNC machine Delrin?
Yes. Delrin is one of the easiest plastics to CNC machine. It cuts cleanly, holds tight tolerances and produces excellent surface finishes without melting onto the tool.
Is Delrin the same as acetal?
Delrin is a brand name for acetal homopolymer (POM-H). Acetal is the generic material family. Acetal copolymer (POM-C) is a different version with better chemical resistance but slightly lower strength.
Which is cheaper, Delrin or Nylon?
Nylon stock is 10 to 20% cheaper. But Delrin machines faster and holds tolerances better. For tight-tolerance parts, Delrin may be cheaper total. For simple parts, Nylon saves money.
What temperature can Delrin handle?
Delrin handles continuous temperatures up to 180 °F. Nylon 6/6 goes to 220 °F. If your part sees temperatures above 180 °F, Nylon is the better choice.
Is Nylon FDA approved for food contact?
Yes. Both Nylon 6/6 and Delrin are FDA compliant for food contact. Both work in food processing equipment, conveyor parts and packaging machinery.
When should I use PEEK instead?
Use PEEK when your part faces temperatures above 400 °F, harsh chemicals, or needs to replace metal. PEEK costs 10 to 20 times more than Delrin or Nylon, so only use it when the environment demands it.
