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PU (Polyurethane) O-rings

-40 °C to 80 °C

Polyurethane O-rings offer excellent mechanical resistance, wear and abrasion resistance. Ideal for dynamic high-pressure hydraulic applications.

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Temperature and chemical compatibility

Temperature and chemical compatibility

Temperature range: -40 °C to +80 °C (short-term up to +100 °C).

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Typical applications: high-pressure hydraulics, pneumatics, abrasive environments, mining and construction machines, pistons and rods.

PU (Polyurethane)

Each elastomer has different mechanical and chemical properties.

PU (Polyurethane) — properties and applications

Polyurethane (PU) is a harder, mechanically resistant elastomer that differs from ordinary sealing materials above all in its strength. PU O-rings have a hardness of typically 90 ShA — that is, they're harder than ordinary elastomers — and they're distinguished by exceptional resistance to wear, abrasion and tearing. As a result they withstand high pressures and suit situations where the seal is exposed to constant mechanical stress. The operating temperature of PU O-rings is −40 to +80 °C (briefly up to +100 °C).

The material offers excellent resistance to mineral oils and mineral-based hydraulic fluids and copes well with cold water; in fuels (especially those containing aromatics or ethanol) and in HFD fluids its resistance is limited. PU's biggest advantage, though, is its mechanical strength: resistance to being extruded from the groove (extrusion) is significantly higher than with ordinary rubbers, so at high pressures it often replaces the combination of a soft O-ring with a back-up ring. This is precisely why polyurethane is at home in dynamic hydraulics and piston seals.

Watch its limits, though. Polyurethane isn't suitable for hot water and steam (hydrolysis and breakdown of the material occur), for temperatures above +80 °C, or for acids and bases. When choosing a material, therefore, always consider which media and temperatures the O-ring will actually be exposed to — this is exactly where it's decided whether PU is the right choice. If your operation exceeds the temperature ceiling or works with steam or aggressive chemistry, reach for a different material — EPDM for steam and hot water (peroxide-cured, but not resistant to mineral oils), HNBR or FKM for oils at higher temperatures.

Typical uses of PU O-rings are high-pressure hydraulics, dynamic and piston seals, and applications with mechanical stress and abrasion where ordinary elastomers wear out faster — typically mining, construction and materials-handling machinery. Compared with the other materials, PU is a specialist in pressure and abrasion, not in chemistry and temperature. If pressure and wear resistance are what matter most in your application — and you're not working with hot water, steam or aggressive chemicals — reach for polyurethane O-rings.

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O-ring material comparison

Indicative values for a quick comparison. Temperature ranges are conservative (continuous service); for a specific medium always verify compatibility or consult a technician.

MaterialTemperature rangeMineral oilWaterAcidFuelHardness (Sh A)Relative price (vs NBR)
NBR-30 – 100 °C Excellent Limited Avoid Excellent70 Sh A1.0×
HNBR-30 – 150 °C Excellent Limited Avoid Excellent75 Sh A3.0×
FKM-20 – 200 °C Excellent Limited Excellent Excellent75 Sh A5.0×
FFKM-20 – 260 °C Excellent Excellent Excellent Excellent75 Sh A50.0×
EPDM-40 – 130 °C Unsafe Excellent Excellent Unsafe70 Sh A1.2×
VMQ-60 – 200 °C Avoid Excellent Avoid Avoid70 Sh A3.5×
PU — your selection-40 – 80 °C Excellent Limited Avoid Limited90 Sh A2.0×

Frequently asked questions about PU (Polyurethane)

Why choose a polyurethane (PU) O-ring instead of ordinary rubber?
Polyurethane is harder and substantially more mechanically resistant than ordinary elastomers — it has exceptional resistance to abrasion, tearing and being extruded from the groove. It therefore suits situations with high pressure and mechanical stress, especially in dynamic hydraulics. Under ordinary conditions, and with aggressive chemistry or high temperature, however, PU isn't the right choice.
What hardness and pressure can a PU O-ring withstand?
Polyurethane O-rings typically have a hardness of around 90 Shore A — that is, they're harder than ordinary elastomers — and that's precisely why they resist high pressures and extrusion into the groove gap well. They're popular in high-pressure hydraulics and piston seals. With the right groove geometry they withstand substantially higher pressures than a soft NBR without a back-up ring.
What damages a polyurethane O-ring?
PU isn't suitable for hot water and steam (hydrolysis occurs), for temperatures above +80 °C, or for acids and bases. Its domain is mineral oils and hydraulics at ordinary temperature, not chemically or thermally demanding environments. If your operation exceeds +80 °C or works with steam, choose a different material.

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