Silicone Foam, Sponge, or Solid Rubber: What’s the Best High Temperature Gasket Material
Silicone has long been regarded as an excellent gasket material because of its resilience, superior temperature stability, and good resistance to the elements present in many types of environments. Its material properties help designers meet their specifications, and the material can be custom fabricated to fit nearly any gasketing application.
When looking at your options for silicone-based gasketing materials, you have three primary choices: silicone foam, silicone sponge, and solid silicone rubber. Silicone foam comes in both an open cell and closed cell material and is known for its high compression set. Silicone sponge is a closed cell foam that is known for its higher tensile strength and tear resistance. Solid silicone rubber adds electrical resistance and even greater strength. Which option is right for your gasketing application? Find out more about your options.
What is Silicone Foam?
Silicone foam is a resilient gasketing material made from liquid silicone rubber, a low viscosity liquid that is extruded and cured in an oven before being fabricated into the desired gasket shape. This results in a foam that is available in many densities (from 12–28 lbs./ft2). The lower density foams are open cell, and the denser foams are closed cell. These types of gaskets can be used in high temperature applications or seals in food processing (meets FDA 21 CFR 177.2600). They can also be used in outdoor settings, as electric vehicle battery seals, and many other applications.
Silicone foam is softer than silicone sponge, but the material has a firmness range that differs depending on the specific silicone foam product. These softer, lower density silicone foams have an open cell structure that can allow liquids to pass, but when compressed, they form a watertight weather seal.
The Pros of Using Silicone Foam
Silicone foam is widely used because of the many benefits it offers:
Flame ratings: carry UL94 V-0 flame ratings.
Low compression set: featuring a UL50/UL50E compression rating, with less compression set than silicone sponge.
Wide temperature range: can operate in lower temperatures than silicone sponge. Service temperatures, depending on the specific product, are generally between -60 and 401-degrees Fahrenheit.
Resistance to UV, ozone, and solvents: UL1571, UL1572, UL157 Oil immersion rating
Thermal insulation: because the material contains more air, it boasts a better thermal insulation than silicone sponge.
Excellent performance: on sealing, cushioning, soundproofing, and other challenging applications.
What is Silicone Sponge?
Silicone sponge is an excellent gasketing and cushioning material that is made from a gum type silicone. Gaskets made from this material are created by vulcanizing the rubber and curing it in an oven. They are ideal for applications with environmental exposure.
Because silicone sponge gaskets are considered closed cell foams, they come in much higher densities that range from 21–43 lbs./ft2. Despite its name, the material does not absorb water, making it widely used in gasketing and sealing applications. The material is naturally waterproof and resistant to high temperatures. Gaskets made from silicone sponge and suited for high temperature applications, food contact applications (meets FDA 21 CFR 177.2600), pharmaceuticals, electronics, outdoor access panels, and many others.
The Pros of Using Silicone Sponge
Silicone sponges offer a wide range of benefits, including:
High flame rating: meets MIL-R-6310 Type II specification and UL 94V-0 flame ratings.
High strength: silicone sponge has a higher tensile and tear resistance than silicone foam. Tensile strength is up to 130 psi.
High operating temperatures: can operate at higher temperatures than silicone foam. Service temperatures, depending on the specific product, are generally between -100 and 500-degrees Fahrenheit.
Better for rugged applications: silicone sponge has higher physical and mechanical properties, making it tougher than silicone foam.
Resistant to UV, ozone, and solvents: making it ideal for outdoor gasketing.
Excellent performance: on sealing, cushioning, soundproofing, and other challenging applications.
What is Solid Silicone Rubber?
Solid silicone rubber is a high temperature vulcanized rubber that has long polymer chains and a high molecular weight. The material is quite flexible, making it ideal for sealing and gasketing applications. The material’s hardness is measured in Shore A and can be manufactured in various degrees of hardness (from 25 to 70 shore A, with 25 being very soft to 70 being hard), and this doesn’t take away from the material’s high strength.
Solid silicone rubber is highly resistant to many environmental conditions, making it an incredibly versatile material that can be used as high temperature gaskets or separators. The material can also be fabricated and sterilized for food contact safe rubber protectors (meets FDA 21 CFR 177.2600), oven seals, etc.
The Pros of Using Solid Silicone Rubber
The ideal use cases for solid silicone rubber involve a high need for:
Electrical insulation: solid silicone rubber can protect against electrostatic discharges and can act as shielding for electronics and electrically sensitive equipment.
High temperature and heat resistance: solid silicone rubber has a very wide operating temperature that lies between silicone sponge and silicone foam (between -80 and 500-degrees Fahrenheit)
Abrasion resistance: rubber is a non-abrasive material that will not scratch or damage sensitive items.
Very high strength: much stronger than silicone sponge and silicone foam, solid silicone rubber can withstand high torque and pressure. The material has a tensile strength of up to 800 psi.
Resistant to UV, ozone, and solvents: high resistances make the material useful in nearly any condition.
Excellent performance: on sealing, cushioning, soundproofing, and other challenging applications.
Choosing Between the Three Options
When choosing between solid silicone rubber, silicone sponge, and silicone foam, take into consideration your applications:
Operating temperature: While all these materials have a wide operating range, silicone foam can resist temperatures of -70°F to 400°F, silicone sponge has the best embrittlement performance resisting temperatures between 100°F - 500°F, and solid silicone rubber has the best high temperature performance withstanding from -80°F to >500°F.
Compression Requirements: silicone foam can be compressed much more than silicone sponge and solid silicone rubber. Silicone sponge has excellent mechanical properties and provides watertight seals with minimal compression.
Needed strength: solid silicone rubber has the highest tensile strength of the three, silicone sponge is next, while silicone foam has the lowest.
Electrical needs: rubber is ideal for electrical applications.
It’s also important to consider flame retardancy, food safety requirements, and many other components of your application. The choice is not easy, but our gasketing experts can help. If you’re unsure what to use for your application, get in touch with our team to talk about your project and specific needs. Contact us today.