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 will be soft and flexible or firm and dimensionally stable. For engineers, mold makers, and product developers, understanding the Shore scale is crucial for the development of functional prototypes and series products.
What is Shore hardness?
Shore hardness is a measure of the indentation hardness of elastomeric materials and is measured in accordance with DIN ISO 7619-1. The measurement principle is based on the indentation depth of a standardized test body under a defined force into the material surface. The deeper the test body 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 pointed cone. This scale is used for very hard rubber compounds and thermosets.
Shore A and Shore D are relevant for silicones, with Shore A covering the main range. The scales overlap to some extent: 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 | 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 castings |
| 20-30 | Soft, flexible | Eraser, soft shoe sole | Flexible molded rubber parts, soft O-rings |
| 30-40 | Medium soft | Car tire tread | Universal impression silicones, standard seals |
| 40-50 | Medium firm | Solid eraser, door seal | Mold making standard, technical seals |
| 50-60 | celebration | Golf practice ball, shoe sole | Precision molds, resilient seals |
| 60-70 | Hard | shopping cart brake | Heavy-duty molds, industrial seals |
| 70-80 | Very hard | Heel of a leather shoe | Special shapes with high stability |
| 80-90 | Extremely hard | Hard plastic transition | Quasi-rigid technical components |
In practice, this means:
- Shore A 15-25: Maximum flexibility, low mechanical strength
- 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 for silicones in practice
Silicone-based elastomers are generally divided into RTV-1 (single-component, moisture-curing) and RTV-2 (two-component, addition-curing or condensation-curing) systems.
RTV-1 silicones are generally in the Shore A 15-50 range. They are supplied ready-mixed and cure through exposure to air humidity.
RTV-2 silicones offer significantly greater 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.
- Elongation at break: Behaves inversely. Softer silicones achieve higher elongation.
- Compression set: Tends to improve with increasing hardness.
- Abrasion resistance: Increases with hardness.
Which Shore hardness for which application?
Mold making and molding
Shore A 20-30 (soft): Ideal for models with deep undercuts and complex geometry.
Shore A 30-40 (medium): The standard in prototype construction 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 a 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 selecting Shore hardness
1. Mold too soft for large castings
A Shore A 20 mold can sag when casting large, heavy parts. Solution: Use at least Shore A 30-40 or provide the mold with a support jacket.
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 consideration of processing temperature
Silicones soften at elevated temperatures. Solution: Choose a harder formulation or use HTV silicones.
4. Confusion between 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: Perform aging tests.
Frequently Asked Questions
Conclusion
Choosing the right Shore hardness is crucial to the success or failure of a silicone application. Shore A 30-50 is ideal for impressions and mold making. For seals, the mechanical load determines the hardness: Shore A 40-50 for static applications, Shore A 60-70 for dynamic applications.
Are you unsure which Shore hardness is best for your application?
Our application engineering 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 will be soft and flexible or firm and dimensionally stable. For engineers, mold makers, and product developers, understanding the Shore scale is crucial for the development of functional prototypes and series products.
What is Shore hardness?
Shore hardness is a measure of the indentation hardness of elastomeric materials and is measured in accordance with DIN ISO 7619-1. The measurement principle is based on the indentation depth of a standardized test body under a defined force into the material surface. The deeper the test body 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 pointed cone. This scale is used for very hard rubber compounds and thermosets.
Shore A and Shore D are relevant for silicones, with Shore A covering the main range. The scales overlap to some extent: 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 | 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 castings |
| 20-30 | Soft, flexible | Eraser, soft shoe sole | Flexible molded rubber parts, soft O-rings |
| 30-40 | Medium soft | Car tire tread | Universal impression silicones, standard seals |
| 40-50 | Medium firm | Solid eraser, door seal | Mold making standard, technical seals |
| 50-60 | celebration | Golf practice ball, shoe sole | Precision molds, resilient seals |
| 60-70 | Hard | shopping cart brake | Heavy-duty molds, industrial seals |
| 70-80 | Very hard | Heel of a leather shoe | Special shapes with high stability |
| 80-90 | Extremely hard | Hard plastic transition | Quasi-rigid technical components |
In practice, this means:
- Shore A 15-25: Maximum flexibility, low mechanical strength
- 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 for silicones in practice
Silicone-based elastomers are generally divided into RTV-1 (single-component, moisture-curing) and RTV-2 (two-component, addition-curing or condensation-curing) systems.
RTV-1 silicones are generally in the Shore A 15-50 range. They are supplied ready-mixed and cure through exposure to air humidity.
RTV-2 silicones offer significantly greater 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.
- Elongation at break: Behaves inversely. Softer silicones achieve higher elongation.
- Compression set: Tends to improve with increasing hardness.
- Abrasion resistance: Increases with hardness.
Which Shore hardness for which application?
Mold making and molding
Shore A 20-30 (soft): Ideal for models with deep undercuts and complex geometry.
Shore A 30-40 (medium): The standard in prototype construction 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 a 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 selecting Shore hardness
1. Mold too soft for large castings
A Shore A 20 mold can sag when casting large, heavy parts. Solution: Use at least Shore A 30-40 or provide the mold with a support jacket.
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 consideration of processing temperature
Silicones soften at elevated temperatures. Solution: Choose a harder formulation or use HTV silicones.
4. Confusion between 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: Perform aging tests.
Frequently Asked Questions
Conclusion
Choosing the right Shore hardness is crucial to the success or failure of a silicone application. Shore A 30-50 is ideal for impressions and mold making. For seals, the mechanical load determines the hardness: Shore A 40-50 for static applications, Shore A 60-70 for dynamic applications.
Are you unsure which Shore hardness is best for your application?
Our application engineering team at SILITECH will be happy to advise you personally. Contact us for a free initial consultation and sample delivery.
