Polyurethane vs. rubber: which one for your part?
A practical comparison of cast polyurethane elastomer and rubber for bushings, bump stops, pads, and wear parts: abrasion, oil resistance, compression set, temperature, cost, and when each material wins.
Request a quoteEngineers reach for rubber out of habit. It is what the factory used, it is cheap in volume, and it is familiar. Cast polyurethane elastomer is the material people switch to after the rubber part fails. Here is how they actually compare.
Where polyurethane wins
Abrasion and tear. This is urethane’s headline property. Wear pads, scraper blades, and rollers in urethane last several times longer than the same part in rubber. If your part is being worn away, switch.
Oil, grease, and fuel. Natural rubber swells and softens in oil. Urethane does not care. Under a vehicle, around a machine tool, or near hydraulics, this alone is often the reason to change.
Ozone and weathering. Rubber cracks and chalks in sun and ozone. Urethane stays intact for years outdoors.
Compression set. A rubber bump stop that gets hit a thousand times ends up shorter. Urethane returns to shape. For anything that carries load repeatedly, this means the part keeps doing its job.
Load capacity. At the same hardness, urethane carries more load than rubber. That lets a designer use a smaller part or a softer one for the same job.
Hardness range. Cast urethane spans roughly 40 Shore A to 75 Shore D in one process. Rubber tops out around 90 Shore A before it becomes brittle.
Tooling cost. Cast urethane runs at low pressure in aluminum or even silicone molds. Rubber compression and injection molds are steel and cost many times more.
Where rubber still wins
High heat. Continuous service above roughly 180 to 200 °F favors silicone or EPDM. Urethane softens.
Hot water and steam. Ester-based urethanes hydrolyze in hot, wet conditions. Ether-based systems do much better, but for steam service rubber is safer.
Very high volume, very simple shapes. For millions of identical, simple parts, rubber compression molding can be cheaper per piece once the steel tool is paid off.
Rebound and grip. For applications that need a dead, non-bouncy feel or high friction, some rubbers are better tuned.
The middle: vibration isolation
Both materials isolate vibration. Rubber generally has more inherent damping at a given hardness. Urethane can be formulated for high damping too, and it holds its properties longer in oil and ozone. For an engine mount pad or a machine foot, we usually recommend pouring samples in two or three durometers and testing. Prototype tooling makes that cheap.
A quick decision guide
| If the part… | Choose |
|---|---|
| Wears away, slides, or gets scraped | Polyurethane |
| Lives in oil, fuel, or grease | Polyurethane |
| Carries repeated compression loads | Polyurethane |
| Sits outdoors for years | Polyurethane |
| Runs continuously above 180 °F | Rubber or silicone |
| Sees steam or hot water | Rubber, or ether urethane with testing |
| Needs millions of identical simple parts | Compare tooling and piece price |
Replacing a rubber part with urethane
You do not need to redesign. Send the rubber part. We will match the geometry, recommend a hardness that gives the same feel with better life, and pour samples. If the rubber part had bonded metal, we bond the same insert in during the pour. Request a quote to start.
