Silicone strength is closely related to the durability, safety and compliance of your silicone products. Therefore, we have prepared this guide for you. We hope this can help you select the appropriate strength of silicone to meet your customer satisfaction.
5 Core Indicators of Silicone Strength
Tensile Strength
Definition: It refers to the maximum force that the silicone material can withstand per unit area at the moment when it is stretched until it breaks or cracks. This represents the material’s capacity to bear load in the stretching direction.
Typical Range: For different types of silicone, their tensile strength varies. The tensile strength of HCR(High Consistency Rubber) generally ranges from 4.0 to 12.5 MPa; while that of FSR(Fluorosilicone Rubber) can reach 8.7 to 12.1 MPa. The range of LSR(Liquid Silicone Rubber) is quite wide, spanning from 3.6 to 11.0 MPa.
Importance: The tensile strength of the silicone rubber is of vital importance for the seals and pipes you produce. The higher the tensile strength is, the less likely your product is to encounter problems during long-term use.
If your silicone products are mostly used in high-pressure pipelines, the excellent tensile strength can prevent potential safety hazards caused by material cracking.
Tear Strength
Definition: When you make a small cut on a silicone material and apply a tearing force, the ability of the silicone material to prevent the cut from getting larger or tearing is known as tear strength.
Typical Range: In terms of tear strength, the lower limit of FSR is higher, while the upper limit of HCR is higher. Generally speaking, the tear strength range of HCR is 9 – 55 kN/m, while that of FSR is 17.5–46.4 kN/m, and that of LSR is 11.5–52 kN/m.
Importance: If you are involved in the production of seals and gaskets, you will know that these products are prone to minor scratches and cracks when being installed, compressed, vibrated, or subjected to repeated deformation.
If the tear strength is insufficient, the crack will rapidly expand, leading to direct tearing, fracture, sealing failure, and leakage. Therefore, for products subjected to dynamic forces and prone to damage, this is a very crucial performance.
Hardness
Definition: Hardness measures a silicone material’s resistance to indentation or deformation when pressed by a hard object.
If the surface of your silicone product is hard and does not leave marks when pressed, it indicates a high level of hardness. If your silicone product feels soft to the touch and indents when pressed with force, it indicates a lower level of hardness.
Typical Range: Hardness is not fixed by the silicone type. You can modify it by adjusting the filler ratio, curing time and temperature. The hardness range of silicone rubber is typically between 10 and 80 Shore A.
10–30 Shore A is low hardness and the silicone is relatively soft with high elasticity. When your silicone ranges from 40 to 60 Shore A, it is of medium hardness, which can balance flexibility and strength. Shore A values ranging from 70 to 80 indicate high hardness and good wear resistance.
Importance: Due to the different hardness of the silicone you use, the feel, structural stability and applicable scenarios of your product will all change accordingly. Hardness is one of the main factors determining your product line.
Elongation at Break
Definition: This refers to the percentage by which the length of the silicone material increases when it is stretched until it breaks.
Typical range: The elongation at break of HCR has the widest range, typically ranging from 90% to 1120%; the upper limit of the range for FSR is relatively low, with a range of 159% to 699%; the lower limit of the range for LSR is as high as 220%, and the upper limit is approximately 900%.
Importance: The elongation at break determines the toughness and deformation resistance of your silicone products. The higher the value, the easier the silicone is to stretch and bend without breaking, which directly affects the durability of the product and the success rate of assembly.
However, if you only pursue products with high elongation but at the expense of strength, they may be prone to deformation.
Compression Set
Definition: The compression set refers to the phenomenon where you place a silicone product under high temperature and compression for a long period of time, and measure the permanent deformation remaining after release.
Grade Range: The compression set does not have a specific range defined based on the type of silicone. It mainly depends on the performance of your silicone product. The compression set for the ordinary grade is approximately 30% – 50%, for the high-quality grade it is about 15% – 25%, and for the high-performance grade, the compression set is less than 15%.
Importance: The compression set is a hallmark of high-quality sealing silicone. If the deformation is smaller, the rebound will be better, especially for seals, which indicates that the seal will last longer.
What Factors Affect Silicone Strength?
Reinforcing Filler
Silicone itself has poor mechanical properties, so you can enhance its strength by adding reinforcing fillers. Below, we will introduce two commonly used reinforcing fillers.
Fumed Silica: Its fineness is relatively high. If you use this reinforcing filler and mix it with silicone for molding, the strength of the silicone will be better. For example, if you want to produce high-toughness silicone, you would use the fumed silica. The silicone made with this material can achieve a tensile strength of 8-10 MPa.
Precipitated Silica: If your requirements for silicone products are not very high, you can use this reinforcing material to make ordinary mixed silicone. It can also enhance the strength, but the enhancement effect is not as good as that of the fumed silica. The strength is relatively lower.
However, it should be noted that adding fillers to the silicone rubber does indeed enhance its mechanical properties. But more is not always better; there is an optimal amount that provides the best results.
When the content of the filler you add is too high, the filler particles will aggregate, which will instead lead to a decline in the mechanical properties of the silicone. Moreover, when you increase the amount of silica, you will also find that the hardness and compression set properties of the silicone will also increase.
Structure Control Agent
The structure control agent can help you improve the bonding state between silica and the rubber compound when reinforcing fillers are added, and prevent the occurrence of structuring. We recommend using siloxanes as the structural control agent because of their strong adaptability.
No matter which type of siloxane you choose, it can effectively improve the dispersion effect of the filler and stabilize the internal structure of the vulcanized silicone. This enables a significant improvement in your silicone’s tear strength and durability.
Polymer Network Structure
We will introduce how to control the strength of silicone through the three core dimensions of the polymer network structure.
Crosslinking Density: The higher the crosslinking density, the tighter the connection between the silicone molecules, and the denser the overall internal network. As a result, the hardness of the silicone product you obtain will be higher.
Vinyl Content: You can add vinyl-containing organic compounds to enhance the tear resistance of the silicone. We suggest adding 3 to 5 phr of a vinyl-containing compound. If too much vinyl content is added, it will damage the stable structure of the silicone, thereby reducing the aging resistance of your silicone products.
Molecular Chain End Group Structure: Polymers with vinyl-terminated end groups, which are mostly used in addition-curing systems. If you use this type of polymer, you can make the silicone have better reaction activity and crosslinking efficiency during the curing process.
Curing Parameters
The curing parameters mainly refer to the curing time and temperature. During the production process of silicone, you can adjust the curing time and temperature to control the hardness of the finished product.
And this will not affect the other properties of the silicone, such as its stretching, tearing, and elasticity, thus maintaining the original characteristics of the silicone material stable.
If you want to further enhance the overall strength of the silicone products and improve the compression set performance, you can perform post-cure on the silicone. This step can effectively eliminate the small molecule volatile substances within the silicone and complete the cross-linking reaction.
Requirements for Silicone Strength in Various Applications
Due to the diverse uses of silicone products in various industries, the required strength for these products also varies. Below is the specific application-related table that we have compiled:
| Application Field | Tensile Strength (MPa) | Tear Strength (kN/m) | Hardness (Shore A) | Elongation at Break (%) | Compression Set (%) | Other Key Requirements |
| Industrial Seals / O-rings | 6–10 | Medium to High (≥25) | 40–70 | 250–500 | ≤20 (22h/175°C) | Low compression set |
| Medical Devices | 7–12 | Medium to High | 30–60 | 300–600 | ≤25 (22h/100°C) | ISO 10993 biocompatibility |
| Automotive Parts | 8–12 | High (≥30) | 50–80 | 200–400 | ≤20 (22h/150°C) | Oil resistance, heat resistance |
| Consumer Electronics (Buttons / Watch Bands) | 5–8 | Medium | 40–70 | 300–600 | ≤30 (22h/100°C) | Comfortable touch, wear resistance |
| Baby & Kitchen Products | 6–10 | Medium | 30–60 | 400–700 | ≤40 (22h/100°C) | FDA food-grade certification |
| Electrical Insulation Components | 4–8 | Low to Medium | 40–70 | 200–500 | ≤30 (22h/150°C) | High dielectric strength |
| Shock Pads / Buffering Components | 4–7 | Medium | 20–50 | 400–800 | ≤25 (22h/70°C) | High resilience |
| Aerospace Parts | 8–12 | High (≥40) | 40–80 | 250–500 | ≤15 (22h/175°C) | Stable performance in wide temperature range |
How to Verify Silicone Strength?
Request the Complete TDS
When purchasing silicone, you can ask the supplier to provide you with the complete TDS (Technical Data Sheet). In addition, it is necessary to ensure that the document clearly indicates all performance indicators, corresponding test standards, and detailed test conditions, such as the testing speed, compression set testing temperature, etc.
This way, you can avoid receiving only general and typical numerical values.
Request Third-Party Test Report
If you rely solely on the internal inspection reports produced by the manufacturer, there may be data discrepancies and risks. Therefore, you can request them to provide batch inspection reports based on the ASTM or ISO international standards. Below are the performance indicators we have compiled along with the corresponding test standards:
| Performance Index | Test Standard |
| Tensile Strength | ASTM D412, ISO 37 |
| Tear Strength | ASTM D624, ISO 34-1 |
| Shore A Hardness | ASTM D2240, ISO 48-4 |
| Elongation at Break | ASTM D412, ISO 37 |
| Compression Set | ASTM D395 Method B, ISO 185-2 |
Apply for Free Samples
You can apply to your potential cooperating suppliers for free silicone samples. After you receive the samples, you can independently entrust a reputable third-party institution to re-test the strength performance of the silicone according to the common industry standards of ASTM or ISO.
Don’t forget to keep the bulk product samples. This way, you can establish long-term data comparisons and be able to track any issues promptly.
FAQ
Is the Tensile Strength Data Provided by Suppliers Typical Value or Minimum Value? Which Is More Useful for Decision-Making?
Typical Value is the average or median value selected by the supplier after multiple tests, and it can reflect the expected performance under the best process conditions. If you are still in the initial stage of comparing different types of silicone products, you can refer to this value.
Minimum value represents the lower limit for this batch of goods. It indicates that the tensile strength of the silicone in this batch must be higher than this value. If you find that the tensile strength of the received silicone rubber is lower than this value and the contract stipulates, you can request compensation from the supplier.
How to Select Temperature and Time Conditions in Compression Set Testing?
If you are producing silicone products for use in room temperature environments, then conduct the test at 70°C for 22 hours; if it is a kitchen appliance or a silicone part that comes into contact with hot water, then test it under at 100°C for 22 hours.
If it is a sealing component for the car engine compartment, the test conditions should be 150°C for 22 hours; for high-end silicone products such as those used in aerospace and high-power electronic equipment, the suitable test conditions are 175°C for 22 hours.
Does Silicone Color Affect Its Strength?
This may have an impact, especially the addition of inorganic pigments may lead to a decrease in the tear strength of the silicone. However, if it is black silicone and carbon black is added, it will instead enhance the tensile properties of the silicone.
Why Do Some Silicone Products Have High Tear Strength but Unremarkable Tensile Strength?
This is normal because tear strength and tensile strength are two different properties. The tear strength can be enhanced by using special polymer additives, but these have a relatively minor impact on the tensile strength.
Can Silicone Strength Test Results of ASTM and ISO Be Directly Compared?
No. Because the sample types, stretching rates and other details used in the two tests are all different, but the test results usually show a fixed deviation. If you have difficulty in determining the strength of the silicone provided by different suppliers, it would be best to ask the suppliers to provide two sets of standard data at the same time.
Final Thoughts
Legensilico is a professional manufacturer of silicone materials, capable of providing you with high-strength and high-quality silicone products as well as customized services. If you think our products are suitable for your business, please feel free to contact us to discuss potential cooperation.
