Nylon vs Delrin vs HDPE for CNC Machining: Full Properties & Application Guide
- Shubh Poojara
- Jun 23
- 7 min read
Nylon, Delrin, and HDPE are three of the most commonly CNC-machined engineering plastics — and three of the most frequently confused. On the surface they look similar: all white or near-white, all tough, all machinable, all in the same cost bracket. But in service they behave completely differently. The engineer who defaults to nylon for a precision bushing in a humid environment, or specifies Delrin for a chemical process component, will eventually have a warranty return.
This guide is a complete delrin vs nylon vs HDPE comparison for CNC-machined parts, based on properties data and what we see on our shop floor handling CNC plastic machining services for engineering customers across industries.
Table of Contents
Why Nylon, Delrin, and HDPE Are So Often Confused
All three are white engineering plastics available in rod, sheet, and slab. All three machine acceptably, cost similarly per kilogram, and serve structural and mechanical applications. The confusion arises because their surface appearance and workability are similar — but their critical properties diverge significantly once you look past machinability.
Moisture sensitivity: Nylon absorbs 2–3% moisture by weight from ambient air, causing 0.2–0.3% linear dimensional growth. Delrin absorbs <0.2%. HDPE absorbs <0.01%.
Chemical resistance: HDPE resists virtually everything. Nylon resists oils and fuels but not strong acids. Delrin fails in strong alkalis and oxidising acids.
Dimensional precision: Delrin holds ±0.05mm on turned features routinely. Nylon drifts with humidity. HDPE has springback on bores.
Impact resistance: Nylon is the most impact-resilient. HDPE second. Delrin is stiffest and most brittle under impact loading.
Nylon (PA6/PA66): Properties, Strengths, and Limitations for CNC Machining
Nylon is a polyamide with excellent tensile strength, fatigue resistance, and toughness. It's self-lubricating to a degree, making it popular for gears, bushings, and wear pads where dry-running is intermittent. It resists oils, fuels, and many solvents — and it's cost-competitive with both Delrin and HDPE in standard rod and sheet stock.
The Moisture Problem — Why Nylon Dimensions Drift After Machining
Nylon's critical limitation for precision applications is hygroscopic dimensional change. PA6 absorbs approximately 2.8% moisture by weight at 65% relative humidity; PA66 absorbs ~2.5%. This causes linear dimensional change of 0.2–0.3%. For a 50mm diameter bore machined to ±0.05mm, moisture-induced growth can push the bore out of tolerance within days of installation in a humid environment.
For context on how moisture uptake and material shrinkage behave across plastic grades, that reference covers the full picture. For machined nylon parts, the practical rule is: machine after conditioning at the working environment's humidity, and note bore tolerance expectations on the drawing.
Nylon vs Delrin: Strength and Impact Resistance
Nylon PA66 has higher tensile strength (~80 MPa) than Delrin (~70 MPa) and significantly better impact resistance. For parts that absorb shock — cam followers, high-torque gears, and impact-loaded structural brackets — nylon's ductility is an advantage Delrin doesn't offer.
When to Choose Nylon Over Delrin
Parts that see impact loading or shock forces where Delrin would crack
Components in contact with oils, fuels, and lubricants
Applications where the moisture environment is controlled and dimensional drift is managed in the tolerance callout
Cost-sensitive high-volume parts where PA6's slightly lower price vs Delrin matters at scale
CNC machined nylon PA66 gear and bushing components — typical nylon vs Delrin application selection scenarios
Delrin (Acetal/POM): The Precision CNC Machining Champion
Delrin (DuPont's acetal homopolymer / POM-H) is the most dimensionally stable common engineering plastic for CNC machining. Near-zero moisture absorption (<0.2%), low friction coefficient (0.20 against steel), and excellent stiffness make it the default material for precision mechanical components. Delrin vs nylon for precision work is not a close comparison — Delrin wins on dimensional stability every time.
Delrin vs Nylon: Dimensional Stability and Tolerances
Delrin holds ±0.05mm on turned diameters as a routine tolerance. Bores machined to close fits stay in tolerance whether the part sits in a dry storeroom or a humid production floor. Nylon in the same conditions will drift 0.1–0.3mm over days to weeks as it absorbs moisture. For precision gearboxes, jigs, and fixtures, this makes Delrin the only practical choice.
Delrin vs Nylon Hardness and Wear Resistance
Delrin has Rockwell hardness R120 vs R119 for PA66 — very similar, but Delrin's lower friction coefficient gives it a meaningful delrin vs nylon wear resistance advantage in dry-running contact. Nylon vs Delrin friction in dry sliding: Delrin generates less heat and wears more slowly. In lubricated conditions the gap narrows significantly.
Delrin vs Nylon for Gears and Bushings
For delrin vs nylon gears: Delrin is the standard for precision gears running at moderate torque in dry conditions — lower friction, stable tooth geometry, predictable clearances. Nylon is preferred for high-torque or shock-loaded gears where its toughness prevents tooth fracture.
For delrin vs nylon bushings: Delrin is the standard for close-tolerance bushings (±0.05mm bores) because its dimensions stay stable in service. Nylon is used for heavy-load bushings in applications where slight dimensional variation is tolerable but impact resistance matters more.
Precision gears (moderate torque, dry): → Delrin — lower friction, stable tooth geometry
Impact-loaded or high-torque gears: → Nylon — higher toughness prevents brittle fracture
Close-tolerance bushings (±0.05mm bores): → Delrin — moisture stability ensures fit is maintained in service
Heavy-load bushings in corrosive environments: → HDPE or PTFE-filled nylon depending on chemical contact
Where Delrin Loses
Delrin is weak in strong acid and alkali environments. Concentrated mineral acids, bleach, and oxidising agents attack acetal rapidly. If your part contacts these, specify HDPE. Delrin also doesn't bond well with standard adhesives — mechanical fastening or surface etching is required.
CNC machined Delrin (acetal/POM) precision components — cams, rollers, and close-tolerance bushings machined to ±0.05mm
HDPE: Chemical Resistance Over Precision
HDPE (High-Density Polyethylene) is the most chemically resistant of the three. It handles acids, alkalis, solvents, and industrial process fluids that would attack nylon or Delrin. Food-safe FDA-compliant grades are widely available. UV-stabilised grades survive outdoors for years without coating.
When HDPE Beats Both Nylon and Delrin
Chemical process components: HDPE resists virtually all acids, alkalis, and aqueous solutions. Chemical tanks, pipe fittings, and ducting components.
Food contact: FDA-compliant HDPE grades for food processing equipment and food-contact surfaces where nylon or Delrin may not be approved.
Marine and outdoor: UV-stabilised HDPE resists UV degradation, moisture, and salt water for years without treatment.
Wear pads and conveyor guides: HDPE's smooth low-friction surface and chemical resistance make it ideal for conveyor guides, cutting boards, and wear-surface pads.
HDPE machining note: HDPE has noticeable springback after CNC machining. Bores can close 0.05–0.1mm after the cutter exits. Flag critical bore fits at quote stage so we can adjust the machining strategy and achieve your intended fit.
Nylon vs Delrin vs HDPE: Full Properties Comparison
Dimensional stability: Delrin > HDPE > Nylon. Nylon drifts with moisture; HDPE has springback; Delrin is the most stable.
Chemical resistance: HDPE > Nylon > Delrin. HDPE handles virtually everything; Delrin fails in strong acids/alkalis.
Impact resistance: Nylon > HDPE > Delrin. Nylon is toughest; Delrin stiffest but most brittle under impact.
Delrin vs nylon wear resistance (dry): Delrin > Nylon > HDPE. Lower friction coefficient gives Delrin the edge in dry-running applications.
Delrin vs nylon hardness: Similar (both ~R120 Rockwell R scale) — Delrin marginally stiffer and harder.
CNC machinability: Delrin > Nylon > HDPE. All machine acceptably; Delrin gives cleanest finish and tightest tolerances.
Cost per kg: HDPE typically cheapest, then PA6, then Delrin (PA66 costs slightly more than PA6).
Application Selection Guide
Precision gears, cams, rollers: → Delrin
Close-tolerance bushings (dry or mildly humid environment): → Delrin
Impact-loaded mechanical components: → Nylon PA66
Components in oil, fuel, or lubricant contact: → Nylon
Chemical process fittings, tank components: → HDPE
Food-contact components: → HDPE (FDA-compliant grade)
Marine and outdoor structural parts: → HDPE (UV-stabilised grade)
Humid environments with precision bores: → Delrin or HDPE — avoid nylon
Frequently Asked Questions: Nylon vs Delrin vs HDPE
What is the main difference between Delrin and nylon for CNC machining?
Delrin (acetal/POM) has near-zero moisture absorption and superior dimensional stability — it's the correct choice for precision mechanical parts. Nylon absorbs 2–3% moisture and dimensions drift 0.2–0.3% after machining, but nylon has higher impact resistance and fatigue resistance for shock-loaded applications.
Which is better for gears — Delrin or nylon?
For precision gears running at moderate torque in dry conditions, Delrin is better: lower friction, stable dimensions, predictable tooth geometry. For high-torque or shock-loaded gears where tooth breakage is the failure mode, nylon's higher toughness is an advantage. Most precision gear applications specify Delrin.
What is the chemical resistance of HDPE vs nylon vs Delrin?
HDPE has the best chemical resistance — it resists virtually all acids, alkalis, solvents, and industrial fluids. Nylon handles oils and fuels well but not strong acids. Delrin is the weakest on chemical resistance and fails in concentrated mineral acids and strong alkalis. For chemical process components, HDPE is the correct specification.
Does nylon absorb more moisture than Delrin?
Yes. Nylon PA6 absorbs approximately 2.8% moisture by weight at 65% RH; PA66 absorbs ~2.5%. Delrin absorbs less than 0.2%. This moisture uptake causes 0.2–0.3% linear dimensional change in nylon — significant for precision bore fits and close-clearance components in humid environments.
Which engineering plastic is cheapest — nylon, Delrin, or HDPE?
HDPE is typically the most cost-effective per kilogram. PA6 nylon follows, then PA66, then Delrin. The difference is usually 15–30% between HDPE and Delrin. For high-volume parts where material cost matters, evaluate HDPE or PA6 if the application allows.
Conclusion
The nylon vs Delrin vs HDPE decision comes down to three questions: How precise does the part need to be? What chemical environment will it operate in? How much impact will it absorb? Delrin answers the precision question. HDPE answers the chemical question. Nylon answers the impact question.
Send us your application details and drawing. Our CNC plastic machining services team confirms the right material before you commit, and DFM review is included with every quote.
For a wider view of engineering plastic options, our guide to 12 plastic injection moulding materials covers the full landscape.
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