Guide
UHMW vs HDPE: which polyethylene should a machined part be made from?
UHMW vs HDPE is a choice between two polyethylenes that differ mainly in chain length: UHMW-PE has far longer molecules, which give it much better abrasion and impact resistance and lower sliding friction, while HDPE is cheaper, easier to weld and mold, and adequate where nothing slides or wears. Choose UHMW for wear strips, chain and conveyor guides, chute liners and bushings; choose HDPE for tanks, covers, machine guards and structural plastic parts with little wear.
By Saola Manufacturing engineering team · Published · Updated
Both materials are white, waxy and look the same on the shelf, and both are bought as sheet and rod for machining. The difference shows up in service and in the drawing tolerances. This guide covers how the two are defined, where each one belongs, and what to put on a drawing for a machined polyethylene part, including the thermal growth that catches out drawings copied from metal parts. For acetal, the other common machined plastic, see Delrin vs acetal.
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What is the actual difference between UHMW and HDPE?
Both are linear polyethylene; UHMW is defined by a far higher molecular weight, measured in the standards by solution viscosity, and that changes how it can be processed and how it wears.
ASTM D4020 defines UHMW-PE as linear polymers of ethylene with a relative viscosity of 1.44 or greater, measured by the procedures in that standard, and covers the virgin resin as powder, granules or pellets for molding and extrusion. Ordinary polyethylene molding and extrusion materials, HDPE included, are classified separately under ASTM D4976. Neither standard gives design data; for that, use the stock-shape maker’s data sheet.
The very long chains of UHMW barely flow when melted, so it is not injection molded in normal practice. It is compression molded or ram extruded into sheet and rod, and parts are machined from that stock. HDPE flows, so it is injection molded, extruded, thermoformed and welded easily. For a buyer, that is the first decision point: a high-volume HDPE part may be cheaper molded than machined, while a UHMW part is almost always machined or cut from sheet.
How do UHMW and HDPE compare for wear, impact and friction?
UHMW wins on abrasion, impact and sliding friction; HDPE wins on cost, weldability and moldability; neither is stiff or heat resistant.
A Mitsubishi Chemical Advanced Materials data sheet for a UHMW-PE grade shows the scale of its wear resistance: in a sand-slurry abrasion test run against 1018 steel indexed at 100, the UHMW grade scored 10, a tenth of the steel’s volume loss (Mitsubishi Chemical Advanced Materials, TIVAR ESD FG data sheet, 2024). The same sheet lists a dynamic coefficient of friction of 0.15–0.30 in its ISO test and a melting temperature of 135 °C (data sheet).
| Property | UHMW-PE | HDPE |
|---|---|---|
| Defined by | Relative viscosity 1.44 or greater (ASTM D4020) | Polyethylene molding and extrusion material classes (ASTM D4976) |
| Abrasion resistance | Very high; sand-slurry index 10 against 1018 steel at 100 | Moderate |
| Sliding friction | Low; dynamic coefficient 0.15–0.30 (ISO 7148-2) | Low, but wears faster in sliding |
| Thermal expansion | About 200 µm/(m·K), 23–100 °C | Also high; check the grade data sheet |
| Heat deflection (1.8 MPa) | 42 °C | Also low |
| Processing | Sheet and rod, machined; not normally injection molded | Molded, extruded, welded or machined |
| Relative cost | Higher | Lower |
Grades matter within UHMW. Makers sell reprocessed, filled, antistatic, food-contact and high-temperature versions; the data sheet above is for a carbon-filled antistatic grade made for conveyor parts. Name the grade or its required properties on the drawing, not only “UHMW.”
When should a part be UHMW, and when is HDPE good enough?
Use UHMW wherever the part slides, rubs or is hit, and HDPE where it mainly encloses, covers or holds and nothing wears it.
- UHMW: wear strips, chain guides, star wheels, chute and hopper liners, bushings in dirty or wet environments, guide rails, scraper blades and impact pads.
- HDPE: tank walls and covers, spacers, machine guards, chemical-resistant brackets, and any part that will be welded or that could be molded at volume.
- Neither: precision bearings with tight running clearance, load-bearing brackets that must not creep, or parts that run hot. Acetal or a filled engineering plastic is usually the better choice.
A useful test is to ask what ends the part’s life. If it is wear or impact, the higher material cost of UHMW is usually repaid. If it is cracking, chemical attack or simple obsolescence, HDPE is enough.
What tolerances can machined UHMW and HDPE parts hold?
Looser than the same drawing in metal, because both materials expand a lot with temperature, relax after machining and deflect under cutting and clamping forces.
Thermal growth is the number to work out first. With a linear expansion of about 200 µm/(m·K) from the UHMW data sheet, a 100 mm length changes by about 0.2 mm for a 10 °C temperature change (Mitsubishi Chemical Advanced Materials). A tolerance tighter than that is only meaningful if the drawing states the measuring temperature and the part is soaked at it before inspection.
Practical drawing rules for polyethylene parts:
- State the measuring temperature, for example measured at room temperature after stabilizing.
- Give the loosest tolerances function allows, and reserve tight ones for the few fits that need them.
- For long wear strips, dimension fixing holes as slots or allow clearance so the strip can expand on a metal frame.
- Avoid flatness callouts on thin, wide plates unless they are measured clamped; free-state flatness drifts as internal stresses relax.
- Allow edge breaks and say how stringy machining burrs are to be removed.
What should the drawing and RFQ say for a UHMW or HDPE part?
Material type and grade, color, any food-contact or antistatic requirement, stock form, the measuring temperature, and which tolerances are critical.
A complete material line reads like “UHMW-PE, natural, virgin, [maker grade or equivalent]” or “HDPE sheet, black, UV stabilized.” Add food-contact compliance by regulation if the part touches food; the data sheet above, for example, states compliance with EU regulation 10/2011 for its grade. Add antistatic or conductive requirements with a surface resistivity limit if the part sees static build-up. Ask for the stock supplier’s certificate with the lot, because UHMW and HDPE cannot be told apart by eye.
If the part might be molded later in HDPE, say so in the RFQ; it changes the design rules, such as drafts and wall thickness, more than the material choice does.
Can Saola supply machined UHMW or HDPE parts?
Plastic parts are not on our published capability pages, so whether a UHMW or HDPE part can be supplied is confirmed at drawing review, before any quote.
Our lead CNC plant in Vietnam runs the metal turning and milling described on the CNC milling and CNC turning pages. If your assembly combines a machined metal part with a polyethylene wear strip or bushing, send the whole drawing package and mark the plastic parts; at drawing review we will tell you plainly which parts can be covered and which cannot. New parts that we do supply get a first-article inspection report, and every lot a dimensional inspection record. Send the drawing for a quote.
Frequently asked
Can you tell UHMW and HDPE apart by looking at them?
Not reliably. Both are white or colored, waxy and light. A certificate from the stock supplier is the dependable proof; a lab can confirm by solution viscosity per the UHMW standard.
Can UHMW be welded or glued?
It is hard to bond with ordinary adhesives and difficult to weld because it barely flows when melted. Mechanical fastening with countersunk screws or bolts is the usual method. HDPE welds easily.
Is UHMW food safe?
Many grades are made for food contact and state compliance with FDA or EU regulations, but not all. Name the regulation on the drawing and ask for the grade’s compliance statement.
Does UHMW absorb water and swell like nylon?
Very little. The data sheet above lists water absorption of about 0.1% at saturation (data sheet), so humidity is not the problem it is with nylon; temperature is.
Sources
- ASTM D4020-18, Standard Specification for Ultra-High-Molecular-Weight Polyethylene Molding and Extrusion Materials, ASTM International, 2018
- ASTM D4976-12a (2020), Standard Specification for Polyethylene Plastics Molding and Extrusion Materials, ASTM International, 2020
- TIVAR ESD FG UHMW-PE product data sheet, Mitsubishi Chemical Advanced Materials, revised 2024