HDPE vs Delrin (Acetal): Which Should You Specify?

Q: Does Delrin expand less than HDPE?

Not on the matched sheets: 6.8 vs 6.70 × 10−5 in/in/°F [1] [2] . Some HDPE datasheets list higher values [20] . so check the grade you are buying.

Q: Which is better for acids and bleach?

HDPE , by every chart row above. Acetal is rated only fair at 1% sulfuric acid and is affected by hypochlorite [7] [8] [10]

Q: Does Delrin absorb more water than HDPE?

Yes: 0.25% in 24 hours and 0.9% at saturation vs 0.01% [1] [2] .

Comparison of a precision-machined Delrin gear and a durable HDPE pipe section highlighting differences in engineering tolerances and material texture

Quick answer

Start with Delrin when: the part carries sustained load, slides or rotates (gears, bushings, rollers), runs hot under load, or sees fuels and solvents.
Start with HDPE when: the part sees strong acids, bleach or caustic, stays wet, must be light, or is a large fabricated part where raw material cost dominates.
Check before you commit: centerline porosity in thick Delrin stock, environmental stress cracking in loaded HDPE, and the exact certificate for any food or water contact.

On one distributor’s ASTM datasheets, Delrin 150 has about 2.5 times the tensile strength and flexural modulus of HDPE, at 1.48 times the density [1] [2]. That is the part everyone knows.

Two things the usual comparison gets wrong: long term air service temperature is nearly identical on those sheets (180 °F vs 185 °F), and so is thermal expansion (6.7 vs 6.8 × 10⁻⁵ in/in/°F) [1] [2].

Chemistry, creep and load decide this choice far more than temperature or expansion do.

Matched Property Data

Both columns come from the same distributor, Plastics International, on ASTM methods at 73 °F. Mixing suppliers and test standards is the most common way these comparisons go wrong.

Property	HDPE	Delrin 150 (POM-H)	Ratio (Delrin / HDPE)
Specific gravity	0.96	1.42	1.48
Tensile strength	4,423 psi	11,100 psi (yield)	2.5
Tensile modulus	225,000 psi	450,000 psi	2.0
Flexural modulus	167,000 psi	420,000 psi	2.5
Tensile elongation	1,350 %	25 % (break)	n/a
Izod impact	1.3 ft·lb/in	1.5 ft·lb/in	1.2
Water absorption	0.01 %	0.25 % (24 h), 0.9 % (saturation)	25 to 90
Dynamic coefficient of friction	0.28 (method not stated)	0.2 (ASTM D3702, 40 psi, 50 fpm)	n/a
Heat deflection temperature, 66 psi	180 °F	336 °F	n/a
Max service temperature, long term	180 °F	185 °F	n/a
Max service temperature, short term	190 °F	300 °F (intermittent)	n/a
Thermal expansion (CLTE)	6.70 × 10⁻⁵ in/in/°F	6.8 × 10⁻⁵ in/in/°F	1.0

(“For HDPE column, source: [1]. For Delrin column source: [2]”)

Vendor typical values for comparison, not design allowables.

The HDPE page does not say whether its tensile figure is yield or break, or the method for its Izod and friction values. Ratios are our arithmetic.

How to read it

Strength and stiffness. Delrin is 2.0 to 2.5 times stronger and stiffer. If deflection under load limits the design, this decides it.
Impact is not a clean win for HDPE. Izod values overlap: HDPE (1.3 to 4.8 ft·lb/in) across five supplier datasheets [1], Delrin (1.5 to 2) [2] [3]. The real difference is ductility: HDPE elongation runs from above 100% to 1,350%, Delrin is 25% [1] [2]. HDPE stretches before it fails, so design to a strain limit, not just a stress limit. HDPE’s brittleness temperature is below −100 °F on two datasheets [4].
Temperature. The nominal long term limits are 5 °F apart. The gap shows up under load: heat deflection at 264 psi is 257 °F for Delrin [2] and 165 to 176 °F for HDPE [4] and short term limits are 300 °F vs 190 °F [1] [2].
Thermal expansion. Equal on this pair. Other HDPE datasheets run higher: 10 × 10⁻⁵ in/in/°F on one, 150 to 230 × 10⁻⁶/K on an ISO PE300 sheet [20]. Do not pick Delrin for lower expansion without checking the HDPE grade’s value.
Moisture. HDPE takes up 0.01%. Delrin takes 0.25% in 24 hours and 0.9% at saturation [1] [2]. For tight tolerances in wet service, ask the supplier for conditioned dimensions.
Friction and wear. Friction overlaps: HDPE 0.20 to 0.29 [4], Delrin 0.2 [2]. Delrin’s sheet lists a wear factor of 55 × 10⁻¹⁰ in³·min/ft·lb·hr [3]. We found no comparable HDPE wear factor, so request a K-factor on your counterface before choosing either for a bearing.

Creep Under Sustained Load

This is where the stiffness gap compounds. Both rows are ISO 899-1 tensile creep modulus from Material Data Center resin datasheets:

Resin	Creep modulus, 1 h	Creep modulus, 1,000 h	Retained at 1,000 h
Delrin 100 NC010 (POM-H)	2,900 MPa [5]	1,600 MPa [5]	55 %
Hostalen CRP 100 (PE-HD pipe resin)	850 MPa [6]	360 MPa [6]	42 %

At 1,000 hours the acetal resin holds about 4.4 times the stiffness. These are resin-level values for a molding grade and a pipe grade, and stress and temperature are not stated, so use them to rank the families, not to size a part.

For a press fit, thread, bearing clearance or any load held for months, get creep curves for your stress and temperature from the supplier.

Chemical Resistance

Published charts disagree with each other and test short immersion, not stressed service. Where sources conflict, the table says so instead of picking one.

Exposure	HDPE	Acetal / Delrin
Bleach (hypochlorite)	Satisfactory at up to 6% and 7 to 15% available chlorine [9]	Severe effect for calcium hypochlorite; [7] sodium hypochlorite 5% rated C on a separate Delrin chart (A is best) [8]
Sulfuric acid	Excellent at 60%, good at 98% [10]	1% already rated C (A is best) [8]
Acetic acid	Satisfactory, including glacial [9]	Severe effect at the chart’s undiluted entry; 20% rated fair [7]
Sodium hydroxide	Satisfactory [9]	Fair for NaOH; severe for calcium hydroxide; excellent for KOH on the same chart [7]
Isopropyl alcohol	Excellent [10]	Excellent [7]
Unleaded gasoline	Charts disagree: good in one, [10] fair at room temperature and not recommended at 50 °C in another [11]	Excellent (regular gasoline excellent at room temperature only) [7] [8]
Acetone	Charts disagree: satisfactory in one, [9] unsatisfactory in another [10]	Excellent [7]

Each source uses its own rating scale; we paraphrase its wording.

The acetal chart rates 48-hour exposure [7]. The A-to-D key on the Delrin fittings chart [8] was not visible in our extract; we read A as best, matching the Cal Pac scale.

The pattern: HDPE is the safer starting point for acids, bleach and caustic.

Acetal is the safer starting point for fuels and solvents.

The Delrin 150 shape sheet itself describes it as resistant to hydrocarbons, solvents and neutral chemicals [3].

If it is acetal but the environment is hot water, chlorine or caustic, compare copolymer (POM-C).

Boedeker reports copolymer holds up substantially better in hot water and steam and with chlorine containing sanitizers, with homopolymer about 10 to 15% stronger [12].

Suppliers also rate copolymer better in strong alkaline solutions [22].

See our detailed guide on: Delrin vs. Acetal

If it is HDPE and the part is loaded, check environmental stress cracking (ESC). HDPE resin datasheets quote an ESCR result measured under ASTM D1693 in a 25% Igepal surfactant solution [13], so ask for it when a stressed part meets detergents, oils or alcohols.

Machining and Stock Form

Both machine. Delrin is listed with excellent machinability [2], HDPE is listed as easy to fabricate [1] and a PE300 supplier calls it well suited to CNC routing, milling and welding [20] “Can it be machined” does not separate them.
Dimensional behavior does. Delrin is 2.5 times stiffer in flexure, so it deflects less under tool and clamp pressure. Because expansion is equal on the matched sheets, thermal growth during cutting is not a reason to prefer Delrin. These two points are engineering inference from the data, not tolerance claims. Achievable tolerance depends on geometry, stock and process, so ask your shop to quote it for your part.
Thick Delrin stock can have a low-density center. The Delrin 150 shape sheet warns of centerline porosity, especially in large cross sections [3]. It matters when the center ends up inside a bore, seal face or pressure part.

See our guide on Delrin 100 vs. 150 for how to check.

Delrin 150 stock availability: rod from 0.187 to 10.00 in diameter and plate from 0.031 to 5.00 in thick [3].

For machining delrin material, see Machining Delrin

Machining Delrin Components for a Current Project?

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Food Contact, Drinking Water and Outdoor Use

Neither family is “food safe” as a polymer. Certification attaches to a grade, form, color and condition of use.

	HDPE	Delrin 150
Food contact listing found	Natural and white HDPE sheet listed to FDA 21 CFR 177.1520 and ASTM D4976 [14]	Natural 150 shapes listed to FDA 21 CFR 177.2480, NSF/ANSI 51 and 61 [3]
Limits stated by suppliers	One manufacturer declares 177.1520 compliance for repeated-use food contact under specified food types and conditions of use, says its HDPE natural is not NSF listed, and says NSF 51 compliance can be requested through NSF [15]	The black 150 sheet shows no FDA or NSF line [17], one distributor states 150 is not USP Class VI compliant because of porosity [16]

Outdoor use

One major supplier marks standard white HDPE sheet as not for use outdoors [14], UV-stabilized grades exist in both families, an HDPE resin sold with UV for outdoor applications [18] and a UV-stabilized Delrin 527UV listed by Boedeker [21]. Specify the stabilized grade for either.

Cost per cm³, Not per kg

We do not publish prices because they move by supplier, size and quantity. The density correction does not move.

HDPE is 0.96 g/cm³ and Delrin 150 is 1.42 g/cm³ [1] [2], so a kilogram of HDPE yields 48% more part volume.

Cost per cm³ = price per kg × density.

Illustrative arithmetic, not a market price: if Delrin quotes at 3 times HDPE per kg, it costs about 4.4 times as much per cm³ (3 × 1.42 ÷ 0.96).

Decision Guide

Horizontal decision matrix banner comparing HDPE chemical and impact properties vs Delrin precision gear and mechanical properties.

Your requirement	Start with	Why (data)	Verify before ordering
Gears, bushings, rollers, load-bearing sliding parts	Delrin	2.0 to 2.5× stiffness; published wear factor [2] [3]	Counterface, speed, wear K-factor
Sustained load, press fit, thread retention	Delrin	1,000 h creep modulus 1,600 vs 360 MPa (resin level) [5] [6]	Creep curves at your stress and temperature
Strong acid, bleach or caustic	HDPE	Chart ratings favor HDPE in every acid and hypochlorite row above	Concentration, temperature, ESCR if loaded
Fuels and ketone solvents	Delrin	Rated excellent; HDPE charts conflict [7][10] [11]	Test at service temperature
Hot under load	Delrin	HDT at 264 psi 257 °F vs 165 to 176 °F [2] [4]	Hot water or chlorine present? Consider POM-C
Wet or washdown, minimal swelling	HDPE	0.01% vs 0.25 to 0.9% water uptake [1] [2]	Conditioned dimensions for tight fits
Large, light, formed or welded part	HDPE	Density 0.96 vs 1.42; ductility [1] [2]	Strain limit, UV grade if outdoors
Thick solid Delrin with bore or seal face	Delrin or POM-C	Centerline porosity warning on 150 shapes [3]	Porosity statement for your diameter
Food or drinking-water contact	Certified grade of either	Listings differ by grade, form and color	Current certificate for the lot
Lowest cost for a non-precision part	HDPE	Density-adjusted cost per cm³ (see above)	Quote both routes

Typical Applications

These are the uses suppliers list for each material. Treat them as a sanity check on the decision guide, not a substitute for it.

HDPE:

Water and chemical tanks and vessels [1]
Light-duty wear strips, chain guides and rails [1]
Pipe systems and chemical containers [4]
Food cutting boards [4]
Orthotic and prosthetic devices [1] [4]

Delrin 150:

Gears, bearings, bushings and rollers [2] [3]
Wear pads and structural components [3]
Pump and valve components in moist or wet environments, and fittings [3]
Electrical insulator parts and electrical components [2] [3]
Jigs and fixtures [3]

Note: the two lists are not paired by function.

What to Put on the Drawing and PO

Family and grade, not the polymer name alone. For Delrin, for example, 150 NC010 extruded shape per ASTM D6100 [3]. For HDPE, the resin or shape specification the supplier cites (ASTM D4976 is common) [14].
Color and form: natural vs black, sheet vs rod, thickness or diameter.
Certificates: FDA, NSF or USP statements for the lot, matched to the form and color you are buying.
Thick Delrin: a porosity statement for that diameter or thickness.
UV exposure: require a stabilized grade if the part sees sun.
Test data to request: creep curves for loaded parts, ESCR for stressed HDPE, wear K-factor for sliding parts.

FAQ

Is Delrin stronger than HDPE?

Yes on tensile strength and stiffness: 11,100 vs 4,423 psi, and 420,000 vs 167,000 psi flexural modulus on the same distributor’s sheets [1] [2].
But HDPE elongates up to 1,350% against Delrin’s 25%, and Izod values overlap, so “stronger” is not the same as “tougher.”

Does Delrin expand less than HDPE?

Not on the matched sheets: 6.8 vs 6.70 × 10⁻⁵ in/in/°F [1] [2]. Some HDPE datasheets list higher values [20]. so check the grade you are buying.

Which is better for acids and bleach?

HDPE, by every chart row above. Acetal is rated only fair at 1% sulfuric acid and is affected by hypochlorite [7] [8] [10]

Does Delrin absorb more water than HDPE?

Yes: 0.25% in 24 hours and 0.9% at saturation vs 0.01% [1] [2].

Is HDPE or Delrin food safe?

Both have food contact listings for specific natural grades, with different regulations and limits (table above). Require the certificate for your lot, form and color.

Related Guides

Sources

All sources last checked October 8, 2026. Vendor and chart values are typical or general-guide values, not design allowables or guarantees.

Last Reviewed: October 2026

Usama Ayub

Usama Ayub is the founder of PlasticSpec and a polymer manufacturing engineer with eight years of hands-on industrial experience in PET, PA6, and PA66 fiber and filament yarn production. He writes material property and selection guides for Delrin, Nylon, PEEK, PTFE, UHMW, Polycarbonate, and ABS.

HDPE vs. Delrin