Delrin vs HDPE: Which Engineering Plastic Fits Your Part?
One is a stiff, precise, low-friction engineering material; the other is a tough, cheap, chemically bulletproof workhorse. Here is how Delrin (POM) and HDPE actually compare — with numbers.
IsoCNC Engineering Team
CNC Machining & DFM Engineers · Updated · 12 min read
On this page
Quick Answer
Choose Delrin (acetal homopolymer, POM-H) when the part must be stiff, dimensionally stable, and precise: it is roughly 2.4× stronger in tension (11,000 vs 4,600 psi), more than twice as stiff, holds machining tolerances easily, and runs a friction coefficient near 0.2 for gears and bushings. Choose HDPE when the enemy is chemistry, water, impact, or budget: it absorbs under 0.01% moisture, resists nearly every common acid and base, stretches 400–600% without breaking, and costs about half as much per kilogram. Delrin machines precision parts — gears, bushings, valve internals. HDPE machines big, wet, chemical parts — tanks, guides, food-contact and marine components.
Delrin and HDPE: Two Very Different Plastics
Delrin is DuPont’s brand name for acetal homopolymer (POM-H) — a highly crystalline engineering thermoplastic designed from the start to replace metal in precision mechanical parts. It is dense (1.41 g/cm³), hard, and stable, and it sits in the same family of use cases as nylon and PEEK: gears, bearings, bushings, cams, valve and pump components. Our Delrin material page covers the grades and machining behavior in detail.
HDPE (high-density polyethylene) is a commodity polyolefin — the same polymer family as milk jugs and cutting boards, supplied in industrial sheet, rod, and plate. At 0.95–0.97 g/cm³ it is light enough to float on water, and it is soft, waxy, extremely tough, and almost chemically inert. It is the material of cutting boards, chemical tanks, marine bumpers, and conveyor wear parts.
The two rarely compete for the same part — but buyers compare them constantly because both are cheap, machinable, and stocked everywhere. The honest framing: Delrin is a precision engineering material; HDPE is an environmental survival material. For the wider landscape, see our guide to CNC machining materials.
Delrin vs HDPE: Property Data Side by Side
Published datasheet values tell most of the story: Delrin wins every mechanical and thermal line; HDPE wins water absorption and cost. Elongation cuts both ways — HDPE’s 400–600% is why it is nearly unbreakable in impact, and why it refuses to hold a tight dimension under load.
| Property (ASTM Test) | Delrin / Acetal Homopolymer (POM-H) | HDPE |
|---|---|---|
| Density (D792) | 1.41 g/cm³ | 0.95–0.97 g/cm³ |
| Tensile strength (D638) | 11,000 psi (76 MPa) | 4,000–4,600 psi (28–32 MPa) |
| Tensile modulus (D638) | 450,000 psi | 200,000 psi |
| Elongation at break (D638) | 30–40% | 400–600% |
| Heat deflection temp, 264 psi (D648) | 250°F (121°C) | ~150°F (66°C) |
| Melting point | ~347°F (175°C) | ~266°F (130°C) |
| Water absorption, 24 h (D570) | 0.2% | <0.01% |
| Coefficient of friction (dynamic) | ~0.20–0.21 | ~0.3 (grade dependent) |
| Continuous service temperature | ~200°F (93°C) | ~176°F (80°C) |
| Relative sheet/rod cost | Roughly 1.5–2× HDPE | Baseline — cheapest engineering sheet |
Two numbers deserve a second look. First, the modulus gap — 450,000 vs 200,000 psi — means an HDPE part flexes more than twice as much as an identical Delrin part under the same load, before creep even enters the picture. Second, the heat deflection gap — 121°C vs 66°C at 264 psi — means HDPE parts sag in conditions (hot washdown lines, parked vehicle interiors) that Delrin shrugs off. If your environment exceeds both, the next step up is covered in our PEEK vs Delrin comparison.
Rigidity and Dimensional Stability: Delrin’s Home Turf
Ask a machining buyer why they specified Delrin and the answer is usually dimensional stability, not strength. Delrin absorbs only about 0.2% water in 24 hours — low enough that a part machined on Monday measures the same a year later, in any humidity. It resists creep under sustained load, it springs back from deflection instead of taking a set, and its thermal behavior is predictable enough that shops hold ±0.002–0.005" (±0.05–0.13 mm) on turned and milled Delrin features as a matter of routine.
HDPE fails this job on three fronts at once: its modulus is less than half of Delrin’s, so the part deflects under cutting and clamping forces; it creeps under sustained load; and its thermal expansion is among the highest of any common plastic. HDPE’s water absorption is technically better, but moisture was never why parts missed tolerance — stiffness, creep, and heat were.
This is why the same buyer who happily machines HDPE tank lids will not quote an HDPE gear. For Delrin’s closer rivalry on mechanicals — and the moisture question that decides it — see our Delrin vs nylon comparison.
Friction, Wear, and Bearing Performance
Both are described as “slippery,” but they wear differently. Delrin runs a dynamic friction coefficient around 0.20–0.21 against steel, with the hardness and resilience to keep that surface under real bearing loads. It is the default choice for precision gears, sprockets, cams, bushings, sliding blocks, and low-noise mechanisms, and PTFE-filled grades (Delrin AF) push friction and wear lower still. A Delrin bushing pressed to size stays round and keeps its clearance for years.
HDPE is slippery but soft: friction against steel is higher (~0.3), and under a concentrated bearing load the bore bellmouths and clearances open up. For low-load, sacrificial wear parts — conveyor guides, chain tracks, slide plates, dock fenders — HDPE is excellent because it is cheap enough to treat as a consumable; for severe abrasion, shops jump to UHMW-PE, its ultra-high-molecular-weight cousin. The dividing line is load: loaded precision motion belongs to Delrin; sliding, sacrificial, wet abrasion belongs to the polyethylenes.
Chemical Resistance and Moisture: HDPE’s Home Turf
Flip the environment and the ranking inverts. HDPE resists an enormous range of chemistry — most acids, bases, salt solutions, detergents, and alcohols — absorbs essentially no water, and never corrodes. That is why it is the default for chemical tank components, laboratory fixtures, plating-line parts, food-processing and washdown equipment, and marine hardware. FDA-compliant grades are standard stock, and HDPE hot-gas welds, so machined fittings weld into tank assemblies — something Delrin cannot do.
Delrin is no chemical weakling — it handles hydrocarbons, fuels, oils, greases, and most solvents better than many engineering plastics, which is why it dominates fuel-system and pump internals. Its failure mode is specific: strong acids and strong bases hydrolyze the acetal polymer chain, and chlorinated water at temperature degrades it over time. In oil or solvent, Delrin outlasts HDPE mechanically; in caustic cleaner or dilute acid, HDPE is the only one to quote.
A practical rule for drawings: if the part touches aggressive chemistry, specify HDPE; if it touches fuel, oil, or solvent and must hold a tolerance, specify Delrin. When the environment beats both — steam, strong oxidizers, or continuous heat past either material’s limit — step up the chain with our engineering plastics overview.
Machinability, Tolerances, and the Real Cost Comparison
Both machine without coolant, but behave differently at the cutting edge. Delrin chips crisply, breaks a clean chip, takes sharp threads and fine finishes, and holds the tolerances quoted above without special technique — it is one of the most machinable plastics in existence. HDPE cuts easily but gummy: stringy chips, burrs at edges and hole exits, and deflection away from the tool, so fine threads and tight tolerances need sharp tooling, light finishing passes, and patience.
On cost, separate the resin from the part. HDPE sheet and rod run roughly half the per-kilogram price of Delrin, which makes HDPE the automatic pick for large parts — a 20 kg machined tank lid is a material-cost decision. On small precision parts the arithmetic flips: a 50-gram bushing contains pennies of resin in either material, and Delrin’s faster machining and lower scrap risk usually make the part cheaper even though the material is not. Buy the material the function requires, and let part size decide ties.
The short version we give buyers: precision gears, bushings, cams, valve and pump internals, jigs that must stay true — Delrin. Chemical and tank components, food and washdown parts, marine bumpers, large wear plates, welded fabrications — HDPE. Send us the drawing and operating environment and we will confirm the call: our engineers review every RFQ, typically within 1–2 business days. Get an instant quote to start.
FAQ: Delrin vs HDPE
Is Delrin stronger than HDPE?
By every structural measure, yes. Delrin homopolymer posts a tensile strength around 11,000 psi (76 MPa) against roughly 4,000–4,600 psi (28–32 MPa) for HDPE — about 2.4 times higher — and its tensile modulus of 450,000 psi is more than double HDPE’s 200,000 psi. “Stronger” needs one caveat, though: HDPE stretches 400–600% before breaking versus 30–40% for Delrin, so it absorbs impact and abuse without cracking. Delrin is the stiff, strong, precise material; HDPE is the soft, tough, forgiving one.
Which is cheaper, Delrin or HDPE?
HDPE is clearly cheaper per kilogram — distributor sheet and rod pricing typically runs around half the cost of Delrin, and HDPE is often the least expensive engineering plastic sheet you can buy. But part cost is not resin cost. On a small precision component, material is a minor line item next to machining time, and Delrin machines faster and holds tolerance without rework. On a large part — a tank lid, a big wear plate, a machined fixture — the resin volume dominates and HDPE’s price advantage becomes decisive.
Can HDPE replace Delrin in gears and bushings?
For loaded, precision, or long-life duty, no. HDPE’s lower modulus lets gear teeth deflect and bores go out of round, its friction coefficient runs higher (~0.3 vs ~0.2 for Delrin), and it creeps under sustained load, so backlash and press fits drift over time. Where HDPE does work in wear service: low-load, low-speed parts — conveyor guides, slide plates, chain tracks — especially in wet or chemical environments that would attack other plastics. For anything that must keep its geometry under load, Delrin remains the default.
Which material handles moisture and chemicals better?
HDPE, decisively. It absorbs under 0.01% water in 24 hours — effectively zero — and resists a very wide range of acids, bases, salts, and detergents, which is why chemical tanks and lab fixtures are made from it. Delrin absorbs about 0.2% in 24 hours and is stable enough that it never meaningfully changes size, and it resists solvents, fuels, and oils well. Its weakness is strong acids and bases, which attack the acetal polymer chain. Wet, corrosive, or washdown service favors HDPE; oily, solvent, or fuel service favors Delrin.
What temperature limits do Delrin and HDPE have?
Delrin is the hotter-running material by a wide margin. Its heat deflection temperature at 264 psi is about 250°F (121°C), it carries a continuous service rating near 200°F (93°C), and it melts around 347°F (175°C). HDPE deflects at only about 150°F (66°C) under the same load, is typically rated for continuous service around 176°F (80°C), and melts near 266°F (130°C). Neither is a high-temperature plastic — if your environment exceeds these ranges, look at PEEK instead — but Delrin has roughly 55°C more working headroom.
When should I choose HDPE over Delrin for a machined part?
Choose HDPE when the environment or the geometry rules Delrin out. The triggers: aggressive chemical exposure (acids, caustics, cleaning agents); constant water or steam-adjacent service; food-contact requirements, since FDA-compliant HDPE is everywhere; large parts where material cost dominates the quote; impact-heavy applications where toughness beats stiffness; and assemblies that will be welded, because HDPE hot-gas welds into tanks and fabrications while Delrin is not practically weldable. If the part is big, wet, chemical, or sacrificial, HDPE is usually the right call.
Related Resources
304 vs 316 Stainless Steel: Which Grade for Machined Parts?
304 vs 316 stainless steel compared for CNC machined parts: composition, corrosion resistance (PREN), machinability,…
6061 vs 5052 Aluminum: Which Alloy for Your Parts?
6061 vs 5052 aluminum compared: strength, machinability, bending, welding, corrosion, anodizing, and 2026 prices —…
6061 vs 6063 Aluminum: Machining vs Extrusion
6061 vs 6063 aluminum compared: strength, machinability, extrudability, anodizing, and selection rules — why…
How to Outsource CNC Machining to China, Step by Step
How to outsource CNC machining to China, step by step: vet suppliers, compare landed cost, control quality remotely,…
Delrin or HDPE? Send the Drawing.
IsoCNC machines Delrin, HDPE, UHMW, nylon, PEEK, and a dozen other engineering plastics — precision gears and bushings to ±0.002" or chemical-resistant fabrications, with material certs and inspection reports on every lot. Not sure which material your environment demands? An engineer reviews every RFQ, typically within 1–2 business days.