Silicone rubber’s flexibility, temperature resistance, biocompatibility and more make it highly effective in many applications. It is commonly used in automotive applications for seals and in medical devices and in kitchenware, as well as in pet products, and more. However, it is not a one-size-fits-all solution. Its limitations become apparent under certain conditions or under forces that it was not designed to endure, causing failure, leaks, or unnecessary expenses.
When it comes to choosing materials, the earlier that these red flags can be identified, the better off engineers and product teams are. This guide outlines five common scenarios where silicone may not be the best choice and suggests practical alternatives. Understanding these constraints supports choosing silicone for the right applications and avoids costly redesigns or field issues down the line.
Red Flag #1 – High Exposure to Petroleum-Based Oils, Fuels, or Strong Solvents
Petroleum-based oils, fuels, and many industrial solvents are incompatible with silicone. It will swell, soften, lose its mechanical strength or stick to the surface and crack and deform over time in continuous contact.
Where Oil and Fuel Exposure Makes Silicone a Poor Choice
It is a common problem in the automotive and industrial field. Common examples are gaskets or seals in direct contact with gasoline, diesel, mineral oils or degreasers. The same type of issues can occur in the fuel system, as well as in the oil pump, as swelling reduces the ability to seal and leads to leaks over time.
Better Alternatives for Oil and Fuel Environments
Nitrile rubber (NBR) is recommended for these applications for moderate temperature oil resistance. Fluoroelastomer (FKM/Viton) is a superior performance in aggressive oils, fuels and chemicals. Fluorosilicone (FVMQ) provides a compromise between the broad range of temperature performance and enhanced fluid resistance, but has not the same degree of resistance to heavy hydrocarbons as FKM. The most suitable option is determined by the specific temperature, concentration and pressure specifications.
Red Flag #2 – Extreme Abrasion, High-Friction, or Heavy Wear Applications
Typically, silicone has a lower abrasion resistance and tear resistance than a variety of engineering elastomers and thermoplastics. It wears, tears or loses shape under repeated rubbing, sliding or impact than is expected.
When Abrasion and Wear Will Quickly Damage Silicone Parts
Wear pads on moving equipment, in high friction mechanical interfaces (pistons, rotating shafts), or in sliding seals against metal or hard plastic. Accelerated surface degradation is also observed with outdoor products or high cycle consumer products.
Better Alternatives for High-Wear and High-Friction Applications
Polyurethane (PU) is outstanding for abrasion resistance and toughness. TPE/TPU is suitable for grips and protective pads. Engineering plastics such as nylon, POM or PTFE may be better than silicone for low friction interfaces. With some designs, protective coatings or minimized contact area can add to the life of silicone, but material changes often are more effective.
Red Flag #3 – Ultra-Tight Tolerances and Precision Mechanical Interfaces
Silicone is soft and flexible which makes maintaining very tight tolerances difficult. Due to molding variations, compression set and thermal expansion, precision-fit applications are difficult.
When Tight Tolerances Make Silicone Difficult to Use
In mechanical interfaces, components with tolerances measured in microns face the problem of having to fit into very small cavities that have tolerances of only a few microns, or of parts that have to maintain perfectly set tolerances when repeatedly compressed. It is common that such situations can cause fitting problems or poor performance.
Better Alternatives for Precision and Tight-Tolerance Applications
Tight tolerances are well maintained in engineering plastics like POM, PEEK or nylon. A metal is the ultimate in precision when rigidity is a requirement. Hybrid designs, that is, using silicone in an appropriate role with plastic or metal in the precision interface, are suited to the best of both worlds.
Red Flag #4 – Structural, Load-Bearing, or High-Stress Applications
The tensile and tear strength of silicone is relatively low. Has a tendency to stretch out permanently, rip or distort under sustained loads and isn’t a structural material used primarily.
When Load-Bearing Requirements Make Silicone Unsuitable
Silicone shouldn’t be used for structural supports, heavy load-bearing pads, or seals that are supposed to withstand high pressure and mechanical force without substantial deformation. These limitations are easily revealed under weight-bearing condition in particular.
Better Alternatives for Structural and Load-Bearing Applications
Use engineering plastic materials such as PEEK, nylon or POM for load carrying parts. Metals continue to be the preferred choice for the highest demand structural components. Moderate loads can be handled by harder elastomers or thermoplastics. Despite the fact that silicone contributes little to the strength of the assembly, it can serve as cushioning or sealing in hybrid structures.
Red Flag #5 – High-Pressure Dynamic Sealing Without Special Design or Material
Silicone performs best in static applications. In high-pressure dynamic sealing involving repeated movement, it risks extrusion, rapid wear, heat buildup, and loss of sealing force.
When Dynamic Sealing and High Pressure Make Silicone Risky
Silicone is used best in static applications. It has a tendency to be extruded, wear quickly, heat up, or lose the sealing force in high pressure dynamic sealing with repeated movement.
Better Alternatives for High-Pressure Dynamic Sealing
Typical failure areas are cyclic movement of hydraulic or pneumatic seals, dynamic connectors and actuators under pressure, and cyclic movement of pneumatic or hydraulic seals. It is hard to handle and the material is prone to extruding or wearing out too quickly in such conditions.
How to Recognize These Red Flags Early in Your Design Process
Before making silicone decisions, follow this quick checklist:
- Does the part come in contact with petroleum oils, fuels or strong solvents?
- Will the part be subjected to excessive abrasion, friction or wear?
- Are there ultra tight tolerances or precision fits to be involved in the part?
- Will the part be subjected to structural loads or high stresses?
- Is the part to be used for high pressure dynamic sealing?
If any of these answers is “yes”, it indicates that it is necessary that the material is carefully evaluated or that alternative materials were used.
When to Talk to a Silicone Manufacturer About Material Alternatives
Communicate in detail the application requirements (temperature, chemistry, mechanical loading, cycle life and regulatory requirements) with an experienced manufacturer early on. A trustworthy partner will openly discuss whether silicone is the best option or if there are alternatives (or a hybrid solution) to silicone that would be better. This transparency eliminates downstream issues and makes the product more relevant to its actual use.
Alright, so there’s something that silicone is not good for.Aha, there’s a time when silicone is not right.
Summary – Know When Silicone Is NOT the Right Choice
The five red flags are:
- Exposure to high levels of petroleum oils, fuels or strong solvents.
- Excessive abrasion, friction or wear.
- Precision mechanical interfaces and ultra-tight tolerances.
- Structural, load-bearing, or high stress applications.
- Dynamic and high pressure sealing, no special design or material.
In many applications, particularly in situations involving temperature extremes, flexibility, or biocompatibility, silicone continues to be a superior option. Knowing its limitations just helps engineers select silicone in the appropriate application and to produce reliable products over time. However, if you are ever in any doubt, it is always best to consult with the knowledgeable manufacturer for the quickest path forward.
