When selecting a silicone part design, it’s important to consider how the silicone will be stressed in the real environment over time. A formulation that works well in a controlled environment under specific conditions can deteriorate rapidly in the outdoors where the UV conditions and temperature fluctuations are different, and a seal that works well in stationary use may fail quickly if it is moved and rubbed repeatedly.
These are real-life conditions that can impact material selection, durometer, geometry, compression set, and project lifespan – and need to be analyzed at project start. From designing silicone parts for appliances to protective sleeves for outdoor equipment to parts for industrial machinery, learning to match silicone part design to your application environment helps avoid costly field failures and warranty claims.
Two Key Environment Dimensions: Indoor/Outdoor and Static/Dynamic
There are two basic dimensions that most determine performance differences between silicone parts: the level of exposure (indoor vs outdoor) and the type of motion (static vs dynamic). These factors all play a role in actual applications, and will be the primary stresses the part will encounter: UV radiation, thermal cycling, moisture, friction, or compression.
Temperature, chemicals and pressure are other factors that can be considered, but the grade and geometry of the material are typically determined by indoor/outdoor and static/dynamic conditions. Imperial City apartments do not remain in good condition if they are not taken care of.
Why These Dimensions Matter More Than Others
The weathering resistance requirements are determined by indoor/outdoor exposure and the abrasion/fatigue requirements are determined by static/dynamic use. These two factors can affect the hardness to be used, surface finish, and even if standard silicone will work or not and what kind of compound should be used.
Indoor Environments – Milder Conditions, Different Design Priorities
It is generally the case that the temperatures inside an application are more stable (typically 10°C to 40°C), the UV exposure is low to moderate, and the humidity changes are not as great as the outside environment. Chemical contact is usually limited to mild cleaners or occasional solvents. Such milder conditions provide designers with greater material choice and flexibility to optimize the costs without compromising performance.
Indoor Silicone Applications Where Design Focuses on Comfort and Basic Sealing
Examples of such uses indoors are refrigerator door gaskets, seals in a microwave, soft-touch covers in electronic equipment, and pads for medical use in a climate controlled environment. In such situations comfort, softness, good compression set, and low cost of production become more important.
Lower durometer silicones (30-50 Shore A) are often used on the grips or mats for better sealing under low pressure and greater comfort to the user. Standard grades are effective since UV and extreme weathering are not issues, and the tooling and material costs will remain low.
Outdoor Environments – UV, Weather, and Temperature Swings
The silicone components are exposed to the direct effects of the sun, temperature variations (sometimes as low as -20°C to as high as 60°C), rain, humidity, dust, possible pollutants, and salt air. Although silicone is often more resistant to UV rays than many other elastomers, these stressors can cause aging of the part if it is not correctly specified.
Outdoor Silicone Parts That Must Resist UV, Temperature and Moisture
Common applications in the outdoor industry are lighting gaskets, connectors for lighting in the automotive industry, equipment protective sleeves, sensor housings, and seals. In these parts, it is important to use UV-stabilized silicone compounds or specially formulated varieties. Geometry should be designed to promote drainage of water, and should not have areas that hold water, and should consider thermal expansion, so as to not crack during freeze-thaw cycles.
More durometer or reinforced compounds may be better for longer service life. Surface finishes may be provided to help to repel dirt and water.
Static Conditions – Lower Movement, Lower Wear, Different Design Rules
Static applications are those where the parts are generally not subjected to flexing or sliding movements, and are primarily under compression or constant contact after being installed. This results in increased service life under compression set if this is a consideration.
Design Considerations for Static Silicone Seals and Pads
With static seals, a compression set is important, as the seal must retain its sealing capacity for many years. Lower shore A-type materials tend to be used for low pressure applications, and a compression percentage of 30-40 percent is generally satisfactory. Slightly higher tolerances may be acceptable because there is no constant movement to exacerbate misalignment problems.
They can be found in gaskets for enclosures, appliance door seals, anti-slip pads under stationary equipment, etc. The emphasis is on uniform sealing and long-term elasticity instead of abrasion resistance.
Dynamic Conditions – Movement, Friction and Repeated Flexing
Dynamic applications include applications involving relative motion (sliding, rotating, reciprocating or repeated bending). This creates friction, heat and fast wear which reduces the lifespan of the product unless there is a design solution to combat these.
Design Considerations for Dynamic Silicone Seals and Moving Parts
Dynamic seals usually require a higher durometer material (between 50 to 70 Shore A) to decrease wear and friction. Typically compression will only be in the range of 10-30% to prevent excessive abrasion. Gland design, a surface finish of mating parts, and lubrication (when possible) are important to avoid tearing or excessive heat. Tight tolerances enable performance for thousands of cycles.
They can be found in pneumatic systems, in systems with moving components such as valve seals, tool grips that bend and flex many times and cable sleeves that are constantly bent. Often heat management and abrasion resistant formulations are critical.
Combining Environment Dimensions – Indoor Static, Outdoor Dynamic, etc.
It is rare that components in the real world fall into a single category. Most applications involve a combination of indoor/outdoor exposure as well as static or dynamic behavior, which must be addressed by balanced solutions.
Example Scenarios and Design Responses
- Indoor + Static: A refrigerator gasket must have an excellent compression set and food grade. UV resistance is not a factor, so normal silicone optimized for softness provides a good long life, low cost, sealing.
- Indoor + Dynamic: Internal seals of office machines undergo repeated motion in controlled indoor environments. Abrasion resistance and heat dissipation become more important and outdoor weathering additives are not needed.
- Weather: Lighting gaskets on external fixtures must be able to endure weather conditions but are not likely to experience a lot of movement. Good compression set, water-shedding geometry and UV-stabilized silicone ensure that there is no degradation or leaks.
- Outdoor + Dynamic: Seals for portable outdoor equipment are subject to exposure to the elements as well as repeated plugging and unplugging. This worst case scenario requires the use of UV resistant, abrasion resistant compounds, strong geometry and correct durometer for flexibility vs. durability.
Material and Geometry Choices Based on Environment
The material, geometry decisions are driven directly by the environment. For outdoor use, it is recommended to use UV stabilised or platinum cured silicones that have been proven for weathering performance. Some dynamic applications require increased hardness or particular low friction compounds.
Geometry follows too: Squeeze is lower on static parts but higher on dynamic parts; sharp edges and points that focus stress must be avoided on dynamic parts; chamfers are needed on dynamic parts; good gland fill is needed on dynamic parts. Water traps should be avoided and thermal movement should be taken into account for outdoor designs.
When Silicone Is a Good Choice and When It Is Not
Silicone is highly resistant to UV/weather and has broad temperature range applications, making it ideal for many outdoor and high temperature applications. In very abrasive dynamic applications, however, other elastomers or changes in design (e.g., using fewer parts or using secondary lubrication) might be more suitable. When necessary, variants of fluorosilicone can be used to overcome aggressive chemical environments.
Practical Checklist – Questions to Ask About Your Environment
Here are some questions to consider before finalizing a design:
- Is the part to be used indoors, outdoors, or in a combination?
- What would be the low and high forecast temperatures?
- Will it be exposed to the direct UV rays of the sun?
- Does the area have exposure to rain, humidity, salt, pollutants?
- Is the part stationary (static) or is it moving back and forth (dynamic)?
- How many cycles/years of service is needed?
- What if the part fails – safety risk, down time or just an inconvenience?
By answering these, you can better match silicone part design with the application environment, and choose the right silicone material, hardness, and geometry from the beginning.
Summary – Environment First, Then Material and Geometry
The best silicone parts are those that have been specified by first defining the actual application, determining the stresses and elements that will dominate it, and finally choosing the grade, durometer, compression, and shape of the part. This method will help avoid many common failures and save on the total cost of ownership with longer service life and less downtime for replacement.
Our engineering team has assisted numerous customers with these decisions and applied in the automotive, consumer, medical and industrial fields. Our in-house mold making capabilities, full testing and years of experience ensure parts for real world application, not theoretical specs.
For projects with custom silicone parts, provide your environmental needs and let us help you design for performance and life.
