Polyurethane Shore Hardness Chart and Selection Guide

What Shore Hardness Actually Measures

Shore hardness is a standardized measure of a material's resistance to permanent indentation. It was developed by Albert F. Shore in the 1920s and remains the industry standard for elastomers and semi-rigid polymers.

The test uses a durometer, a device with a calibrated spring-loaded indenter that is pressed into the material surface for a fixed duration. The method is governed by the ASTM D2240 standard, which defines the precise indentor geometry, spring force, and testing procedure for each scale.

For polyurethane, two scales are used regularly.

Shore A

Shore A measures softer, more flexible materials. It uses a truncated cone indenter and is the standard for most elastomeric parts: seals, gaskets, wheels, rollers, and protective liners.

The Shore A scale runs from 0 to 100. In practice, polyurethane parts for industrial use typically fall between Shore A 40 and Shore A 95.

Shore D

Shore D measures harder, more rigid materials. It uses a sharper, pointed indenter and applies to compounds that are near-plastic in rigidity.

Shore D is used for harder polyurethane components: structural bushings, wear plates, and parts that need to resist deformation under very high loads without any meaningful flex.

A rough equivalence between the two scales: Shore A 100 is approximately Shore D 50, though the relationship is not perfectly linear.

Urethane Hardness Scale: How Shore A and Shore D Compare

The urethane hardness scale is not a single continuous line. It is made of two overlapping durometer scales, each running from 0 to 100, that use different indenters and spring forces. A reading on one scale cannot be converted exactly to the other; the equivalences in the chart above are approximations based on where the two scales overlap.

• Shore A covers soft to hard elastomers. Most polyurethane parts, including industrial rollers, polyurethane wheels and bumpers and gaskets, are specified on this scale.
• Shore D covers harder, near-plastic compounds. It is used once a material becomes too hard for the Shore A indenter to give a meaningful reading.
• The overlap zone sits roughly between 90A and 100A, which corresponds to the low end of Shore D (about 40D to 50D). Under ASTM D2240, readings above 90 on one scale are less reliable, so the next harder scale is preferred.

In practice, a specification such as 95A and one such as 45D describe very similar materials. What matters is that the supplier and the buyer use the same scale, and that the hardness is confirmed on the finished part. For abrasive service such as polyurethane liners and screens, hardness is often chosen across this overlap zone, depending on particle size and impact.

How Shore Hardness Affects Performance

Load-bearing capacity

Harder compounds distribute load over a smaller area and resist deformation better. A Shore A 90 wheel will carry significantly more weight without flattening than a Shore A 60 wheel of the same dimensions.

For applications where the part carries sustained heavy loads such as industrial carts, conveyor systems, and crane wheels, hardness in the Shore A 80-95 range is typically required.

Abrasion resistance

There is a general correlation between shore hardness and abrasion resistance, but it is not absolute. Polyurethane compounds in the Shore A 70-95 range tend to offer the best abrasion performance. Very soft compounds, while excellent for shock absorption, wear faster under sliding contact with abrasive materials.

Parts like dust seal rings for gyratory and cone crushers are often formulated in the mid-to-high Shore A range to balance sealing flexibility with resistance to abrasive dust and debris.

Sealing and compression

Seals and gaskets need enough flexibility to conform to mating surfaces without requiring excessive force. Too hard, and the part will not seal properly. Too soft, and it will deform permanently under pressure.

Most sealing applications fall in the Shore A 50-80 range, depending on pressure, surface finish, and whether the seal is dynamic (moving) or static.

Noise and vibration

Softer formulations absorb vibration more effectively. If noise reduction or shock isolation is a priority, compounds in the Shore A 30-60 range tend to perform better. This is common in material handling equipment and anywhere metal-to-metal contact needs to be damped, for example with a polyurethane bumper or a urethane compression spring.

Matching Hardness to Your Application

If you are selecting a compound for a new part or replacing an existing one, work through these criteria:

• What loads will the part carry? Higher sustained loads call for harder compounds.
• Is abrasion or surface wear the primary failure mode? Mid-range Shore A hardness typically offers the best wear resistance.
• Does the part need to flex or compress to function? Seals and gaskets require enough softness to conform.
• Is vibration or impact a factor? Softer compounds dampen shock; harder compounds transmit it.
• What is the temperature range? Very low temperatures can stiffen softer polyurethane; formulation adjustments may be needed.

For a practical breakdown of how the shore hardness scale maps to polyurethane formulations by hardness range and use case, PSI Urethanes offers a useful reference.

Our team works through these parameters with clients before specifying a compound. The right hardness is not always obvious from the application name alone; it depends on the actual operating conditions.

Why Custom Formulation Matters

Off-the-shelf polyurethane stock is manufactured to cover a broad range of uses. Custom formulations allow for precise tuning of hardness, elongation, tear resistance, and chemical compatibility together, not just hardness in isolation.

Two compounds at Shore A 80, whether cast as a roller cover or as cast urethane bars, can behave very differently depending on the chemistry behind them. One may be more resilient under dynamic loading; another may offer better resistance to specific fluids. This is why hardness is a starting point, not the full specification. Our polyurethane materials page outlines the formulations available, and our comparison of polyurethane vs rubber shows how hardness interacts with the choice of elastomer.

Willsup Inc. has been manufacturing custom polyurethane parts since 1971, with in-house design and machining capabilities that allow for precise part geometry and compound selection. Whether you need a standard formulation or something tuned for a specific environment, the process starts with understanding what the part actually needs to do.

Conclusion

Shore hardness is the starting point for any meaningful polyurethane part specification. Understanding the difference between Shore A and Shore D, and knowing which range maps to your application's load, wear, and sealing requirements, prevents costly mismatches between material and environment.

If you are unsure which shore hardness fits your application, contact us for guidance on compound selection tailored to your operating conditions.

FAQ

What is the difference between Shore A and Shore D hardness?

Shore hardness is measured on two scales. Shore A covers softer, more flexible elastomers and is used for most polyurethane seals, wheels, and rollers. Shore D covers harder, more rigid materials and applies to structural components and wear plates. The two scales overlap at the high end of Shore A and the low end of Shore D, with Shore A 100 roughly equivalent to Shore D 50.

What shore hardness is best for polyurethane wheels and rollers?

Most industrial wheels and rollers are specified between Shore A 70 and Shore A 95. The exact value depends on load capacity, rolling speed, and the surface material in contact. Higher hardness offers better load-bearing capacity and abrasion resistance, but reduces vibration dampening. For heavy-duty conveyor systems or mining equipment, the upper end of that range is typically the right starting point before refining based on operating conditions.

What is the ideal Shore hardness for a polyurethane roller?

Most polyurethane rollers fall between Shore A 60 and Shore A 95. Softer rollers, toward 60A to 80A, give more grip, run quieter and protect delicate conveyed products. Harder rollers, toward 85A to 95A, carry heavier loads, resist abrasion and hold their shape under sustained pressure. For conveyors handling abrasive material, 70A to 95A is the usual range. Our custom polyurethane rollers page lists the options available.

Can I specify shore hardness when ordering a custom polyurethane part?

Yes. When ordering custom parts from a manufacturer like Willsup Inc., you can specify a target hardness range, and the formulation will be selected to match it. The manufacturer should also ask about sustained load, operating temperature, chemical exposure, and whether the part is dynamic or static. Shore hardness is the starting point, but the full operating environment determines which compound is actually appropriate for your application.