Choosing the Right Shore Hardness: Explained from 0A to 90A
Shore hardness is one of the most important material properties when selecting silicones. It determines whether a component becomes soft and flexible or firm and dimensionally stable. For engineers, mold makers, and product developers, understanding the Shore scale is crucial for developing functional prototypes and series products.
What is Shore hardness?
Shore hardness is a measure of the indentation hardness of elastomeric materials and is measured according to DIN ISO 7619-1 . The measurement principle is based on the depth of penetration of a standardized indenter under a defined force into the material surface. The deeper the indenter penetrates, the softer the material and the lower the Shore value.
There are various Shore scales for different hardness ranges:
Shore 00: For very soft, gel-like materials (0-100). The indenter is a ball with low spring force. Typical for soft gels and foams.
Shore A: The most common scale for elastomers (0-100). The indenter is a truncated cone. It covers the range from very soft to medium-hard rubber materials and is the standard scale for RTV silicones.
Shore D: For hard elastomers and soft plastics (0-100). The indenter is a sharp cone. This scale is used for very hard rubber compounds and thermosets.
For silicones, Shore A and Shore D are relevant, with Shore A covering the main range. The scales partially overlap: a material with Shore A 90-95 corresponds approximately to Shore D 40-45. RTV silicones typically range between Shore A 0 and Shore A 70.
Shore Hardness Table
| Shore A | Hardness scale | Everyday comparison | Typical application |
|---|---|---|---|
| 0-10 | Very soft, gel-like | Jelly, chewing gum | Softest impressions, skin imitations, special padding |
| 10-20 | Very soft, pliable | Soft bath sponge | Soft seals, medical padding, flexible potting compounds |
| 20-30 | Soft, flexible | Eraser, soft shoe sole | Flexible molding rubbers, soft O-rings |
| 30-40 | Medium-soft | Car tire tread | Universal molding silicones, standard seals |
| 40-50 | Medium strength | Firm eraser, door seal | Mold-making standard, technical seals |
| 50-60 | Firm | Golf practice ball, shoe sole | Precision molds, durable seals |
| 60-70 | Hard | Shopping cart brake | High-load molds, industrial seals |
| 70-80 | Very hard | Heel of a leather shoe | Special molds with high stability |
| 80-90 | Extremely hard | Hard-plastic transition | Quasi-rigid technical components |
For practical purposes, this means:
- Shore A 15-25: Maximum flexibility, low mechanical load capacity
- Shore A 30-40: Optimal compromise for detailed impressions
- Shore A 40-50: Standard in professional mold making
- Shore A 60-70: When mechanical stability is more important than flexibility
Shore hardness of silicones in practice
In silicone-based elastomers, a fundamental distinction is made between RTV-1 (one-component, moisture-curing) and RTV-2 (two-component, addition-curing or condensation-curing) systems.
RTV-1 Silicones are typically in the Shore A 15-50 range. They are supplied pre-mixed and cure through exposure to atmospheric moisture.
RTV-2 Silicones offer significantly more flexibility. They cover the entire range from Shore A 0 (ultra-soft gels) to Shore A 70 (very hard molding compounds).
Relationship between Shore hardness and mechanical properties:
- Tear strength: Typically increases with Shore hardness.
- Tear elongation: Behaves inversely. Softer silicones achieve higher elongations.
- Compression set: Tends to improve with increasing hardness.
- Abrasion resistance: Increases with hardness.
Which Shore hardness for which application?
Mold making and impression taking
Shore A 20-30 (soft): Ideal for models with severe undercuts and complex geometry.
Shore A 30-40 (medium): The standard in prototyping and small-series mold making. Example: SILISIL RTV MF Dura 30 with Shore A 30.
Shore A 50-60 (hard): For precise, dimensionally stable molds with long service life.
Seals and O-rings
Shore A 40-50: Standard range for static seals.
Shore A 60-70: For dynamic seals in pneumatics and hydraulics.
Shore A 70-80: Special applications with high mechanical loads.
Technical components
Shore A 30-40: Vibration dampers, rubber feet, flexible couplings.
Shore A 50-60: Roller coatings, conveyor belt elements, protective padding.
Shore A 60-80: Technical rollers, gears, buffers with high load capacity.
Common mistakes when choosing Shore hardness
1. Mold too soft for large cast parts
A Shore A 20 mold can sag under large, heavy casting masses. Solution: Use at least Shore A 30-40 or provide the mold with a support shell.
2. Mold too hard for complex undercuts
A Shore A 60 mold is difficult to demold. Solution: Choose Shore A 30-40 or design the mold in multiple parts.
3. Shore hardness without considering processing temperature
Silicones become softer at elevated temperatures. Solution: Choose a harder formulation or use HTV silicones.
4. Confusion of Shore A and Shore D
Shore D 40 is significantly harder than Shore A 40. Solution: Always pay attention to the correct scale.
5. No testing of long-term stability
Soft silicones can harden over months due to plasticizer migration. Solution: Conduct aging tests.
FAQ
Conclusion
The correct choice of Shore hardness determines the success or failure of a silicone application. For molding and mold making, the Shore A 30-50 range is optimal. For seals, the mechanical load determines the hardness: Shore A 40-50 for static, Shore A 60-70 for dynamic applications.
Are you unsure which Shore hardness is optimal for your application?
Our application technology team at SILITECH will be happy to advise you personally. Contact us for a free initial consultation and sample delivery.
Choosing the Right Shore Hardness: Explained from 0A to 90A
Shore hardness is one of the most important material properties when selecting silicones. It determines whether a component becomes soft and flexible or firm and dimensionally stable. For engineers, mold makers, and product developers, understanding the Shore scale is crucial for developing functional prototypes and series products.
What is Shore hardness?
Shore hardness is a measure of the indentation hardness of elastomeric materials and is measured according to DIN ISO 7619-1 . The measurement principle is based on the depth of penetration of a standardized indenter under a defined force into the material surface. The deeper the indenter penetrates, the softer the material and the lower the Shore value.
There are various Shore scales for different hardness ranges:
Shore 00: For very soft, gel-like materials (0-100). The indenter is a ball with low spring force. Typical for soft gels and foams.
Shore A: The most common scale for elastomers (0-100). The indenter is a truncated cone. It covers the range from very soft to medium-hard rubber materials and is the standard scale for RTV silicones.
Shore D: For hard elastomers and soft plastics (0-100). The indenter is a sharp cone. This scale is used for very hard rubber compounds and thermosets.
For silicones, Shore A and Shore D are relevant, with Shore A covering the main range. The scales partially overlap: a material with Shore A 90-95 corresponds approximately to Shore D 40-45. RTV silicones typically range between Shore A 0 and Shore A 70.
Shore Hardness Table
| Shore A | Hardness scale | Everyday comparison | Typical application |
|---|---|---|---|
| 0-10 | Very soft, gel-like | Jelly, chewing gum | Softest impressions, skin imitations, special padding |
| 10-20 | Very soft, pliable | Soft bath sponge | Soft seals, medical padding, flexible potting compounds |
| 20-30 | Soft, flexible | Eraser, soft shoe sole | Flexible molding rubbers, soft O-rings |
| 30-40 | Medium-soft | Car tire tread | Universal molding silicones, standard seals |
| 40-50 | Medium strength | Firm eraser, door seal | Mold-making standard, technical seals |
| 50-60 | Firm | Golf practice ball, shoe sole | Precision molds, durable seals |
| 60-70 | Hard | Shopping cart brake | High-load molds, industrial seals |
| 70-80 | Very hard | Heel of a leather shoe | Special molds with high stability |
| 80-90 | Extremely hard | Hard-plastic transition | Quasi-rigid technical components |
For practical purposes, this means:
- Shore A 15-25: Maximum flexibility, low mechanical load capacity
- Shore A 30-40: Optimal compromise for detailed impressions
- Shore A 40-50: Standard in professional mold making
- Shore A 60-70: When mechanical stability is more important than flexibility
Shore hardness of silicones in practice
In silicone-based elastomers, a fundamental distinction is made between RTV-1 (one-component, moisture-curing) and RTV-2 (two-component, addition-curing or condensation-curing) systems.
RTV-1 Silicones are typically in the Shore A 15-50 range. They are supplied pre-mixed and cure through exposure to atmospheric moisture.
RTV-2 Silicones offer significantly more flexibility. They cover the entire range from Shore A 0 (ultra-soft gels) to Shore A 70 (very hard molding compounds).
Relationship between Shore hardness and mechanical properties:
- Tear strength: Typically increases with Shore hardness.
- Tear elongation: Behaves inversely. Softer silicones achieve higher elongations.
- Compression set: Tends to improve with increasing hardness.
- Abrasion resistance: Increases with hardness.
Which Shore hardness for which application?
Mold making and impression taking
Shore A 20-30 (soft): Ideal for models with severe undercuts and complex geometry.
Shore A 30-40 (medium): The standard in prototyping and small-series mold making. Example: SILISIL RTV MF Dura 30 with Shore A 30.
Shore A 50-60 (hard): For precise, dimensionally stable molds with long service life.
Seals and O-rings
Shore A 40-50: Standard range for static seals.
Shore A 60-70: For dynamic seals in pneumatics and hydraulics.
Shore A 70-80: Special applications with high mechanical loads.
Technical components
Shore A 30-40: Vibration dampers, rubber feet, flexible couplings.
Shore A 50-60: Roller coatings, conveyor belt elements, protective padding.
Shore A 60-80: Technical rollers, gears, buffers with high load capacity.
Common mistakes when choosing Shore hardness
1. Mold too soft for large cast parts
A Shore A 20 mold can sag under large, heavy casting masses. Solution: Use at least Shore A 30-40 or provide the mold with a support shell.
2. Mold too hard for complex undercuts
A Shore A 60 mold is difficult to demold. Solution: Choose Shore A 30-40 or design the mold in multiple parts.
3. Shore hardness without considering processing temperature
Silicones become softer at elevated temperatures. Solution: Choose a harder formulation or use HTV silicones.
4. Confusion of Shore A and Shore D
Shore D 40 is significantly harder than Shore A 40. Solution: Always pay attention to the correct scale.
5. No testing of long-term stability
Soft silicones can harden over months due to plasticizer migration. Solution: Conduct aging tests.
FAQ
Conclusion
The correct choice of Shore hardness determines the success or failure of a silicone application. For molding and mold making, the Shore A 30-50 range is optimal. For seals, the mechanical load determines the hardness: Shore A 40-50 for static, Shore A 60-70 for dynamic applications.
Material question still open?
Whether sealing, potting, or bonding, when the application is critical, material selection is not a trivial matter.
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