Shore A hardness is one of the most influential parameters in the performance of any silicone gasket or profile. It determines sealing capability, dimensional stability, the force required for compression and fatigue resistance in static or dynamic applications.
Selecting an incorrect hardness can lead to leaks, permanent deformation, assembly failures or even total loss of system functionality. Unlike other materials, silicone does not respond linearly to compression and does not retain the same stiffness throughout its service life.
1. What is Shore A hardness and why does it matter so much?
Shore A hardness measures the resistance of an elastomer to a standardised pressure applied by a standardised indenter. It is not just a measure of surface stiffness; it reflects a combination of elastic modulus, crosslink density, internal viscosity and the molecular structure of the compound.
For this reason, two silicones with the same nominal hardness can behave very differently in a real application. In the industrial design of gaskets and profiles, hardness acts as an indicator of the effort the material requires to deform and recover its shape.
2. Hardness selection in static applications
In applications without movement — lids, ovens, enclosures, thermal chambers or industrial equipment — hardness determines the force required to achieve sealing without overly deforming the material. The key is to achieve a compression between 20% and 30%.
- Low closing force → 30–40 Shore A
- Standard industrial seals → 40–50 Shore A
- Large sections or structural stiffness → 60–70 Shore A
3. Hardness selection in dynamic applications
Dynamic applications demand a difficult balance between flexibility, mechanical strength and recovery capacity. Machinery doors, repetitive mechanisms, actuators and gaskets subjected to thousands of cycles require a hardness able to absorb deformation without losing dimensional stability.
- Recommended range → 50–60 Shore A
- Higher hardness = greater wear resistance but less adaptation
- Lower hardness = greater flexibility but shorter service life under continuous cycling
4. How temperature affects Shore A hardness
Hardness is tested at 23°C, but the actual behaviour varies considerably with temperature. At high temperatures, soft silicones lose stiffness and reduce sealing force. At low temperatures, the material becomes harder, affecting its ability to deform correctly during assembly.
- Ovens, sterilisers → 60–70 Shore A
- Cryogenic environments → soft compounds with high recovery
- Fluctuating temperatures → thermally stabilised compounds
5. Hardness is not chosen without considering profile geometry
Thickness, shape and cross-section of the profile modify the actual mechanical feel of the material. A 40 Shore A thick wall can respond like a thin 55 Shore A profile due to its overall resistance to deformation.
Hardness does not define the behaviour of a profile; its geometry does.
— Engineering Department – ProSilicones64
6. Key factors for selecting the correct hardness
- Compression available in the design
- Maximum and minimum temperature
- Frequency and type of mechanical cycles
- Profile shape and wall thickness
- Regulatory compliance (FDA, EN 45545-2, ISO 10993)
- Chemical conditions of the environment
- Expected service life and maintenance
7. Most frequent errors when choosing Shore A hardness
- Selecting hardness by intuition or feel
- Selecting a soft material in high-cycle dynamic applications
- Using high hardness without validating sealing capability
- Ignoring the variation of hardness with temperature
- Not considering permanent deformation (compression set)
8. Technical conclusion
Selecting the correct Shore A hardness is not about choosing an arbitrary number, but about understanding how the elastomer interacts with the physical, thermal and geometric environment of the application.
A correct choice avoids premature failures, reduces maintenance and significantly extends the service life of extruded gaskets and profiles in demanding industrial environments.
Need to validate the correct hardness for your project?
Our technical team reviews the drawing, the planned process and the service conditions to define a stable, manufacturable hardness compliant with applicable standards.
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