What does “50-degree silicone” mean?
An informal request for “50-degree silicone” needs clarification: does it mean 50 Shore A? Readings can be compared on the same scale under the same test conditions. A number without a scale leaves the measurement method unspecified.
ASTM International's public explanation of ASTM D2240 describes indentation hardness under defined conditions; indenter geometry and applied force affect the result. Numbers from different scales, such as Shore A and Shore D, should not be directly compared or treated as having a simple universal conversion. Reference: ASTM D2240
A brief can begin with “Shore A is the proposed scale,” followed by agreement on the target, tolerance and method. If only a reference sample is available, describe the feel to retain or change and use it as a starting point.
Why compare other properties when hardness is similar?
Data sheets commonly report hardness, tensile strength, elongation at break, tear strength and compression set separately. Shin-Etsu's silicone rubber product data follow this approach and identify cure conditions. Material selection needs a set of properties; hardness is not a complete performance specification. Reference: Shin-Etsu silicone rubber product data
Organize the comparison around the product's actions:
| Use action | Properties to consider beyond hardness | Sample-validation focus |
|---|---|---|
| Frequent stretching, fitting or removal | Tensile strength and elongation at break | Repeat the actual assembly action and observe cracking or remaining deformation |
| Pulling at thin edges or openings | Tear strength | Check vulnerable part locations, not only a material specimen |
| Prolonged clamping or compression | Compression set and its test conditions | Evaluate under time, temperature and assembly conditions relevant to use |
| Pressing, gripping or bending | Material data and finished-product handling | Compare candidates with the same geometry and record acceptable behavior |
This table helps plan material selection and sample review. It is not a universal hardness standard for these products.
Check test conditions before comparing numbers
Different numbers on two data sheets do not automatically show which material is more suitable.
The public explanation of ASTM D412 notes that tensile properties are affected by extension rate, temperature, humidity, specimen geometry and conditioning; comparisons require consistent test conditions. Tensile properties alone may not directly represent complete service performance. Reference: ASTM D412
For tear strength, check the specimen and method too. ASTM D624 explains that results relate to the particular test conditions and should not be equated directly with service performance. Reference: ASTM D624
For prolonged compression, review compression set. ASTM D395 evaluates retention of elastic properties after prolonged compressive stress, mainly for static compression. Record temperature, duration and method alongside the result. These ASTM references describe the publisher's public explanations, not a reproduction of full testing procedures. Reference: ASTM D395
When a material is described as stronger in tension, more tear-resistant or better at recovering, ask which data support that statement, under what conditions, and whether finished-product validation is also needed.
A four-step sample-validation process
First, describe the use. Identify gripping, covering, stretching, pressing or prolonged compression. Include contacting objects, the environment and the failures that matter most.
Second, compare candidates. Ask the supplier to propose materials for the geometry and application. Keep sample geometry consistent where possible. If wall thickness, shape and material change together, record them separately rather than attributing every difference to hardness.
Third, confirm the documents. Check grade, hardness scale, data sheet and test conditions. Distinguish reference values from the requirements both parties will use for acceptance.
Fourth, retain samples and records. Keep approved samples, drawing revisions, material requirements and validation results together. Later decisions can then use a clear reference instead of repeated requests to make a part “softer” or “harder.”
How to describe the requirement in an inquiry
We are developing a silicone product that will be repeatedly bent and assembled. Attached are a drawing and reference-sample description. We would like to compare different firmness options. Please propose candidate materials for this geometry and provide the hardness scale, relevant material data and test conditions. The target hardness, tolerance and acceptance method will be agreed after sample review.
If a target hardness is already known, include it. Otherwise, state the required function, reference sample and unacceptable outcomes first. This supports a more useful material and sample proposal.
To start a project, review the Zhongding silicone OEM / ODM development process or send drawings, reference samples and use requirements. Begin the material discussion with the actual product needs.