Choosing the right silicone for your mold making directly affects your mold durability, dimensional accuracy, production efficiency, and the quality of your final cast.
We will introduce the 4 key parameters that determine the performance of the silicone, as well as the different requirements for the silicone in different applications, to help you make the best business decision.
4 Technical Parameters for Mold-Making Silicone
When choosing silicone for your mold making, the four key parameters: hardness, tensile and tear strength, viscosity, and demolding time, directly determine the stability and production cost of your product.
Hardness
The hardness of silicone is usually measured in units of Shore A. Shore A hardness measures the flexibility and rigidity of cured silicone. The lower the number, the softer the texture; the higher the number, the harder it is. This directly determines the suitability of the mold for the application and its service life.
The hardness range of silicone is quite wide, and different molds are suitable for different hardness levels. You only need to select the appropriate hardness silicone mold for your business.
Hardness Application Range
If you choose the 0 – 20 Shore A low-hardness silicone, it has a soft texture and can easily be demolded from complex, inverted and intricate shapes. 25 – 40 Shore A grade medium-hard silicone, featuring both flexibility and durability, is suitable for most common applications such as resin pouring and soap molds.
45 – 60 Shore A and above high-hardness silicone has excellent wear resistance and can withstand thousands of demolding cycles. It is highly suitable for your use in mass production, high-pressure conditions, or large component molds.
Tensile and Tear Strength
Understanding these two key indicators: tensile strength and tear strength. They are also very important for you when choosing the appropriate silicone for the mold.
Tensile strength refers to the maximum tensile force that the silicone can withstand before breaking, measured in MPa or psi; tear strength represents the silicone’s ability to resist tearing, measured in kN/m.
Importance
Both of these directly determine the lifespan of your mold. A higher tensile strength will make the mold less prone to damage when being pulled apart during demolding, especially suitable for complex shapes.
Excellent tear strength can prevent minor cracks from expanding, preventing the mold from being damaged rapidly during repeated demolding, and ensuring the stable operation of your long-term batch production.
The table below is the data we have compiled for comparing and recommending the tensile and tear strengths of silicone materials. You can refer to it:
| Parameter | Entry-Level | Industrial Grade (Recommended) | High-Performance Grade |
| Tensile Strength | >3 MPa | >5 MPa | >7 MPa |
| Tear Strength | >8 kN/m | >15 kN/m | >25 kN/m |
Viscosity
The viscosity is a crucial factor in choosing the silicone for mold production, determining your production process and cost. Viscosity is used to measure the fluidity of the liquid silicone after mixing, with units of cps or mPa・s.
It also directly affects your production results: High viscosity silicone may require vacuum degassing depending on mold complexity and mixing conditions. Low viscosity silicone is easy to expel air bubbles and can also penetrate the fine textures of the mold base, perfectly replicating the details.
At the same time, low viscosity silicone flows smoothly when poured, making the operation simpler and more convenient, and can effectively improve your casting efficiency and product accuracy.
Degassing Requirements for Different Viscosity Levels
You can refer to the following table to select the silicone that suits your production process and budget:
| Viscosity Range | Flow Description | Degassing Requirement |
| < 3,000 cps | Watery consistency | Optional (natural air release) |
| 3,000 – 10,000 cps | Honey-like consistency | Vacuum degassing recommended |
| 10,000 – 30,000 cps | Paste-like consistency | Vacuum degassing required |
| > 30,000 cps | Non-flowing / Thixotropic | Degassing may not be necessary for simple brush-on applications, but vacuum degassing is still recommended for detail-critical molds |
Working and Demolding Time
The working time and demolding time are two key parameters that you need to pay close attention to during the production process. Working time refers to the period after Part A and Part B are mixed during which the silicone remains pourable. Once the time exceeds this limit, the silicone will start to thicken and solidify.
The demolding time is the total duration from the mixing stage to the complete solidification and the point where it is safe to remove the mold.
Both of these directly affect the production efficiency of your factory. Short working time and fast curing speed are beneficial for batch turnover, but require rapid processing; long working time offers higher tolerance and is suitable for large or complex molds, but will accordingly prolong the single-piece production cycle.
Typical Time Ranges
When choosing silicone for mold making, there are two major curing systems: condensation silicone and addition silicone.
Addition silicone has a higher cost, but it has an extremely low shrinkage rate, a longer service life, no by-products, and is resistant to high temperatures, making it suitable for precision molds and mass production. However, you should be careful to avoid the influence of contaminants on the curing process.
Condensation silicone has a lower cost, but it has a high shrinkage rate and is prone to aging and contraction, and it releases by-products. It is suitable for manufacturing large quantities of low-precision molds. The working time and demolding time for these two types of silicone you can refer to the following table:
| Curing System | Working Time | Demold Time (Room Temperature) | Accelerated Curing with Heating |
| Tin-cure (Condensation Type) | 20 – 45 minutes | 4 – 8 hours | Heating not recommended |
| Platinum-cure (Addition Type) | 15 – 60 minutes | 4 – 24 hours | 1 – 2 hours at 60 – 80°C |
Silicone Recommendations for Different Mold Applications
Food Grade Molds
If you are making food grade molds, such as baking molds or chocolate candy molds, it is recommended that you use platinum-cure silicone with a hardness controlled within the range of 20-60 Shore A. Soft and easy-to-release molds should be selected at 20-30 Shore A, while baking molds should preferably be 40 – 60 Shore A.
Certifications and Compliance
Because molds for food contact require FDA and LFGB food safety certifications. Food-grade compliance depends on the complete silicone formulation and certification testing, not only the curing system. And platinum-cure silicone is easier to pass the testing and certification, and suitable for the production of various food molds.
Thus, your products can meet the entry requirements of the European and American markets, ensuring the compliance and reliability of your products.
Architectural Decorations and Large-Scale Mold Casting
If you are using architectural mold making or large-scale mold making, platinum-cure silicone is the preferred choice. However, if your cost budget is limited and you are using ordinary decorations or low-melting-point metals, you can also choose tin-cure silicone.
For this type of mold silicone, the hardness should be controlled between 30 – 40 Shore A, the tear strength should be greater than 15 kN/m, and the working time should be no less than 30 minutes.
The higher tear strength can prevent the edges of large molds from cracking and deteriorating. The sufficient operating time can meet the construction rhythm for large-scale pouring. It is suitable for your production needs of batch manufacturing large decorative components.
Certifications and Compliance
If you want to enter the European market, you need to pass the REACH test; for the Chinese market, it is GB/T 40125-2021. ISO 9001 is a quality management system certification, and as an internationally recognized standard, you also need to pass it.
Precision Figurines and Jewelry
If you need precise detail reproduction for figurine or jewelry molds, it is recommended to choose platinum-cure silicone with a softer texture, such as one with a hardness ranging from 10 to 25 Shore A. Moreover, the viscosity of the silicone should be lower than 5,000 cps, and the shrinkage rate should be less than 0.1%.
The low viscosity characteristic enables the silicone to fully penetrate the fine textures, allowing you to fully replicate the details; the extremely low shrinkage rate ensures that the dimensions are precise and stable after molding, avoiding deformation deviations, and meeting your requirements for high-precision mold replication.
Certifications and Compliance
The certification requirements for this type of silicone molds are basically the same as those of the previous category. You can conduct tests such as REACH, RoHS, GB/T 40125-2021, and ISO 9001 according to different market demands. This will ensure that your products can smoothly circulate in various markets.
Prototyping and Fixture Molds for Electronics
In the field of electronics, you can use silicone molds for small-batch customization, prototype development, and the fixture positioning of irregular electronic components.
For electronics prototyping and low-volume production, silicone molds should offer good dimensional stability, moderate heat resistance, and compatibility with commonly used encapsulation materials.
RoHS-compliant silicone materials are often preferred for projects related to electronic components and assemblies.
It is recommended to choose platinum-cure silicone with a hardness of 25 – 40 Shore A. Moreover, the silicone mold can withstand high temperatures. Some potting materials release heat during the curing process, and using a silicone mold is safer for you.
FAQ
How Many Times Can Silicone Molds Be Used?
The tin-cure silicone molds can generally be used 20 to 50 times, while the platinum-cure silicone molds can be used 100 to 1000 times. The number of uses of silicone molds is influenced by multiple factors and there is no definite limit.
In terms of silicone type, platinum-cure silicone has a longer lifespan than tin-cure silicone; from the perspective of casting materials, materials such as resin and gypsum cause less wear than cement and metals; simple molds are more durable than complex molds.
If you use release agents properly and store them properly, you can effectively increase the number of uses of silicone molds.
Will Silicone Molds Shrink? How Much Shrinkage Occurs?
Silicone molds may experience shrinkage, and the shrinkage rate varies depending on the type of silicone.
For instance, the typical shrinkage rate of tin-cure silicone is 0.5% – 1.0%, with moderate dimensional stability; while platinum-cure silicone usually has a shrinkage rate of less than 0.1%, making it more suitable for high-precision mold manufacturing.
What Temperature Is Required for Silicone Mold Curing? Can It Be Accelerated?
The curing process usually takes 4 to 24 hours under a room temperature of 21 – 25°C. Heating at 60 – 80°C can accelerate the curing of platinum-cure silicone, which can be shortened to 1 – 2 hours. However, tin-cure silicone is not recommended to be heated as it may cause bubbles.
What to Do If Silicone Molds Start Deforming After Several Uses?
After using the silicone mold several times, it will deform. This might be because the hardness of your silicone mold is too low. You can replace it with a high-hardness silicone. It could also be that the heat generated during the curing of the casting material causes the silicone to deform. It is recommended that you choose heat-resistant silicone.
Also, store it horizontally to prevent deformation due to compression.
Why Is the Surface of Cured Silicone Molds Still Sticky?
It could be that the silicone you used has expired, or the mixing ratio is incorrect. The mixing ratio of the silicone is based on weight rather than volume. Of course, insufficient stirring during the mixing process or high environmental humidity can cause the silicone to become sticky after curing.
Platinum-cure silicone is sensitive to cure inhibition caused by sulfur-containing clays, amines, latex, and certain tin compounds. You can choose to use tin-cure silicone or apply a barrier coat.
Final Thoughts
Legensilico is a professional silicone manufacturer with over 20 years of experience, and we can provide you with a one-stop service. If you want to customize silicone molds of different specifications or want to learn more about silicone, please feel free to contact us at any time.
