The performance of silicone parts is not only dependent on the grade of the material, but also on the features of the part design: wall thickness, geometry, and the flow of materials during the molding process. Walls which are thicker might need to be cured differently or acquire internal stress. Geometry complexity influences flow pattern, tear resistance and dimensional stability. Poor design can result in voids, shrinkage, warping, or uneven hardness.
Most engineers choose silicone solely on a basis of hardness or grade without paying consideration to the relationship between design features and flow and curing. This usually results into production errors or operational breakdown.
When selecting silicone material, it is important to consider not only the grade of material used, but also the thickness of the walls, the geometry of the parts and the flow properties to ensure high performance, manufacturability and durability.
Part geometry and material flow should be considered in silicone material selection and part design to ensure manufacturability, durability and consistent performance. To gain a better understanding of how these factors are consistent with overall grade evaluation, refer to the guide to the evaluation of silicone provided by HT Silicone.
Why Thickness of Wall Affects the choice of material.
Silicone parts depend on the thickness of the wall to determine the rate of curing, flow, elasticity, and mechanical properties of silicone parts.
Practically, the thickness of the silicone wall directly affects the rate at which heat is transferred through the part during the curing process, and how the material reacts to post-cure shrinkage. Thin sections cure quicker and are more flexible, however, may experience the problem of lower tear resistance during repeated flexing. Thicker parts, however, require slower curing rates to prevent the entrapment of air or internal pores that undermine the final component.
Why Wall Thickness Impacts Material Selection
Silicone parts depend on the thickness of the wall to determine the rate of curing, flow, elasticity, and mechanical properties of silicone parts.
Practically, the thickness of the silicone wall directly affects the rate at which heat is transferred through the part during the curing process, and how the material reacts to post-cure shrinkage. Thin sections cure quicker and are more flexible, however, may experience the problem of lower tear resistance during repeated flexing. Thicker parts, however, require slower curing rates to prevent the entrapment of air or internal pores that undermine the final component.
Effects on Mechanical Performance
The measurements of hardness can be significantly different in thin and thick parts of the same part due to the fact that the material cools and cross-links differently. Compression set – the behavior of silicone losing its ability to recover its elasticity also varies with thickness. A 1 mm wall could be fully recovered after compression whereas a 6 mm wall of the same grade could be permanently deformed unless the curing profile was changed.
Design Considerations by Thickness Range
The engineers dealing with custom silicone products soon discover that it is impossible to ignore these differences and expect the field to work, particularly where consistent sealing of the product or repeated compression is required.
| Wall Thickness | Impact on Silicone | Design Consideration |
| <2 mm | Faster curing, higher flexibility | Ensure adequate tear strength |
| 2–5 mm | Balanced curing and elasticity | Monitor shrinkage and stress |
| >5 mm | Risk of incomplete curing or internal voids | Adjust curing cycle and flow rate |
| Variable thickness | Potential warping or inconsistent hardness | Optimize wall transitions and radii |
Real-World Application Insight
A silicone gasket in consumer electronics accessories: a uniform thickness 1.5 mm wall can be used to allow fast cycle times and excellent flexibility, however adding a 4 mm sealing bead without adjusting the peroxide or platinum cure system of the material can create hard spots or flash. The balancing wall thickness silicone at the first stage of CAD prevents the mentioned issues and enhances the overall durability of silicone.
Part Geometry: How Shape Influences Performance
Part geometry influences silicone flow, stress profile, tear strength and dimensional accuracy.
Geometry determines the location of stress concentration and the flow of the molten silicone in the mold cavity. Acute angles or sudden changes in thickness form weak spots which rip under tension. Tall projections or thin ribs might not fill out or may contract in different directions causing dimensional instability. Deep undercuts or hollow sections further complicate the flow paths creating a higher chance of air traps or knit lines that weaken parts.
Optimizing Geometry for Silicone Behavior
The addition of generous fillets and suitable draft angles drastically reduces the stress concentration and enhances the release of the mold. In more complicated geometries, it will be necessary to choose a grade with a higher tear strength or a better flow.
| Geometry Feature | Impact on Silicone | Mitigation / Recommendation |
| Sharp corners | High stress, risk of tearing | Add fillets or radii |
| Deep cavities | Flow imbalance, incomplete filling | Adjust gate location, flowable grade |
| Thin ribs | Shrinkage or breakage | Increase wall thickness or select higher tear material |
| Hollow or undercuts | Warping or surface defects | Mold design optimization, flow simulation |
Practical Geometry Lessons from the Shop Floor
A simple difference between a 90-degree corner, and a 0.5 mm radius angle can remove tearing during demolding, and increase product life by 3050 percent in accelerated testing. Such small geometry adjustments, combined with the appropriate silicone material choice, can transform what might otherwise be scrapped into high performance, reliable components.
Material Flow During Molding
The silicone flow behavior has an influence on the filling, voids, surface finish, and internal stress.
The flow behavior of silicone is controlled by viscosity, shear-thinning properties, and the type of molding process used, compression or injection of liquid silicone rubber. Grades with low viscosity fill finer details rapidly yet can flash when the gates and vents are not precisely matched. Materials with high viscosity do not flow into long or thin points and create the risk of short shots or knit lines. Quick curing may freeze the material before it drops at the end of a flow path, entrapping internal stresses, which subsequently deform the material.
Key Flow Factors and Process Controls
Temperature of the mold, the pressure of the injection and the position of the gate have to be adjusted to the particular part geometry and wall thickness silicone combination. Flow simulation software is now an inseparable part in this case; it is used to predict where air will become trapped, and where variation in hardness will be visible before steel has been cut.
| Flow Factor | Effect on Part | Design Consideration |
| Low viscosity | Good fill, risk of flash | Control gate and venting |
| High viscosity | Harder to fill, risk of voids | Optimize mold temperature, injection pressure |
| Flow imbalance | Uneven fill, hardness variation | Mold flow simulation, balanced gates |
| Rapid curing | Can block flow | Adjust temperature and material grade |
Early in the design process understanding silicone flow behavior will prevent costly tooling revisions and will ensure consistent curing and flow in silicone across all shots.
Practical Guidelines for Integrating Design and Material Selection
The design decisions should be synchronized with the properties of silicone materials to guarantee performance and manufacturability.
The manufacturability of silicone begins when the wall thickness, geometry and flow are not considered as a separate decision but rather as an interdependent variable. Correlate the curing profile and the thickest part without compromising the thinnest walls to provide the necessary tear strength. On parts with long flow paths or variable geometry, a higher-flowable grade may perform better than a stiffer one even though the datasheet hardness is exactly the same.
Coordinated Strategies for Common Challenges
| Design Factor | Material/Process Strategy |
| Wall thickness | Match curing rate, ensure uniform hardness |
| Sharp corners | Select tear-resistant grade, add fillets |
| Long flow paths | Use higher flowable silicone, optimize injection points |
| Variable geometry | Consider flowable, stable grade, test prototype |
| Surface finish | Material must support finishing method (printing, coating, engraving) |
The surest step in validation is prototyping with the exact desired geometry and thickness. A small production run on a one-cavity tool is often a good measure of the problem that no simulation can adequately forecast.
Common Mistakes
Errors in design or the material used can easily result in defects and functional failures.
The most common pitfalls that we observe are:
- The choice of a silicone grade without taking into consideration wall thickness silicone and its influence on the uniformity of the curing process.
- Silicone features are ignored by ignoring the concentration of stress caused by part geometry silicones.
- Undervaluing flow difficulties in difficult parts with long flow paths or deep cavities.
- Skipping prototype testing with the final geometry and thickness.
- It is assumed that thin and thick sections of the same part will act identically in respect to hardness, shrinkage or compression set.
Any of these errors may cause a good design to be scrapped during production, or, more seriously, fail in the field, which damages customer confidence.
Checklist for Wall Thickness, Geometry, and Flow Evaluation
A checklist helps engineers systematically validate design and material choice before tooling.
Using this checklist before releasing drawings for mold construction dramatically reduces risk and accelerates time-to-market.
| Question | Purpose |
| Are wall thicknesses within recommended range for material? | Ensures uniform curing and performance |
| Are corners and ribs designed to reduce stress concentration? | Prevents tearing and warping |
| Will the material fill cavities and long paths without voids? | Confirms flow adequacy |
| Are variable thicknesses accounted for in material and curing selection? | Prevents hardness or shrinkage inconsistency |
| Has prototype testing validated flow, curing, and performance? | Reduces production risk |
| Is the selected material compatible with part geometry? | Ensures manufacturability and durability |
Conclusion — Design and Material Must Be Evaluated Together
Wall thickness, geometry of the part and flow are critical factors impacting silicone performance. The choice of materials grade should consider the curing, fill, and stress distribution. Vital to the validation of choices are prototype testing and simulation. Design and material choice will minimize defects and provide durability over time.
The choice of silicone material cannot be done without considering the part design. Taking into account the product wall thickness, geometry and material flow combined with the selection of the grade will ensure manufacturability, uniform performance and durability of the product, reducing defects and increasing lifecycle reliability. When these factors are considered as one system, engineers and sourcing teams provide custom silicone products which ensure reliability not only when the products are initially shot but also during years of service.
