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Read moreShore A Hardness of Rubber: How to Choose for Gaskets and Pads
09 October, 2026 | Admin
Short answer: Shore A hardness is a number from 0 to 100 that tells you how hard a rubber is, measured with a spring-loaded indenter called a durometer. Softer rubber (lower numbers) seals rough surfaces at low bolt load. Harder rubber (higher numbers) resists extrusion, abrasion and high pressure. Most rubber gaskets fall around 60–70 Shore A.
How Shore A Is Measured
A Shore A durometer presses a small indenter into the rubber under a spring load. The deeper it sinks, the lower the reading. The method is standardised (for example ASTM D2240 and ISO 48-4). Readings depend on thickness, temperature and how long the indenter is held, so compare values measured the same way.
Typical Hardness Ranges
| Shore A | Feel | Typical uses |
|---|---|---|
| 30–40 | Very soft | Sponge-like seals, low-load gaskets, cushioning |
| 50–60 | Soft | Door and enclosure seals, gaskets on uneven flanges |
| 60–70 | Medium | General flange gaskets, rubber sheet, pads |
| 70–80 | Firm | Higher-pressure gaskets, wear pads, bearing pads |
| 80–90+ | Hard | Rollers, high-pressure seals, abrasion-resistant parts |
Choosing Hardness for Gaskets
- Uneven or light flanges (sheet metal covers, plastic flanges): softer, 50–60 Shore A, seals at lower bolt load.
- Standard pipe flanges: 60–70 Shore A is the common choice.
- Higher pressure: firmer rubber or a reinforced (insertion) sheet resists blow-out and extrusion.
- Thin gaskets generally seal better at higher pressure than thick soft ones.
Choosing Hardness for Pads and Mounts
- Softer pads isolate vibration better but deflect more under load.
- Harder pads carry more load with less deflection.
- Structural bearing pads are specified by hardness grade with defined load and shear properties; see our bridge bearing pads.
Hardness Is Not the Whole Story
Two rubbers with the same Shore A can behave very differently. The compound (NBR, EPDM, neoprene, silicone), compression set, temperature and chemical resistance all matter. Pick the compound first, then the hardness. See NBR vs EPDM vs neoprene rubber sheet.
Temperature Effects
Rubber gets harder in the cold and softer in heat. In Gulf conditions, surface temperatures in the sun can be high, so allow for a softer feel in service than at room temperature, and check the compound’s temperature rating.
Ordering Tips
- State the hardness with a tolerance, typically ±5 Shore A.
- State the compound, thickness and any approvals.
- For pads, state the load and allowable deflection.
Related: rubber gaskets for piping, flange gasket types and EPDM rubber sheets. For the full selection process, see our guide on how to choose engineering plastic. Products: rubber sheets and polyurethane products. Every order from Diode Trading EST is supplied with a Material Test Certificate.
Quick Selection Guide
If you are not sure which hardness to order, these general rules are a good starting point. Always confirm against the equipment manufacturer or the project specification.
- Low-pressure flanges, uneven or painted surfaces: softer sheet (around 50 to 60 Shore A) seals more easily with low bolt load.
- General-purpose gaskets and seals: medium hardness (around 60 to 70 Shore A) is the most common choice and balances sealing with resistance to extrusion.
- Higher pressure, wear pads and impact areas: harder sheet (around 70 to 80 Shore A) resists extrusion, cutting and abrasion better.
- Anti-vibration pads and mounts: choose hardness by load per pad; a softer compound isolates more vibration but deflects further.
When you order rubber sheet from Diode Trading EST, tell us the compound, the hardness, the thickness and the size you need. We confirm the hardness on the Material Test Certificate supplied with every order.
Frequently Asked Questions
What Shore A hardness is best for gaskets?
Most flange gaskets use 60–70 Shore A. Softer rubber suits uneven or light flanges; firmer rubber suits higher pressure.
Is higher Shore A better?
Not always. Harder rubber resists pressure and abrasion but needs more bolt load to seal and isolates vibration less.
How is Shore A hardness measured?
With a Shore A durometer, following standards such as ASTM D2240 and ISO 48-4.
What tolerance applies to Shore A hardness?
Commonly ±5 Shore A, unless the specification states otherwise.
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