Is Silicone Foam, Sponge or Solid Rubber the Best High Temperature Gasket Material?
Needing a high temperature gasket material is not uncommon. If you’re looking for long-term sealing performance in demanding environment, whether you're sealing components in an HVAC system, appliance, EV batteries, vehicle, or electronics enclosure, silicone-based materials are highly leveraged solutions for their thermal resistance, durability, and stability.
Even within the material category of “silicone”, you still have options. Silicone foam, silicone sponge, and solid silicone rubber have their own strengths, weaknesses, and ideal applications, giving you a variety of material options that can be used in different applications.
What is silicone, why does it perform so well under pressure and heat, and how can you choose the right silicone gasket for your application?
How Silicone Maintains High Heat Resistance
Silicone is a synthetic elastomer composed of a silicon-oxygen backbone (Si-O-Si), with various organic side groups that modify its properties. It’s generally known as a hybrid plastic and rubber, but its properties can change based on how it’s made (specifically if it’s made into silicone foam, sponge, or rubber). Unlike carbon-based polymers like natural rubber or polyurethane, silicone’s inorganic backbone gives it exceptional resistance to extreme temperatures, oxidation, ozone, UV radiation, and many chemicals.
Silicone's temperature resistance typically ranges from –55°C to +232°C (–67°F to +450°F), with some formulations capable of withstanding up to +315°C (600°F) intermittently. Its unique molecular structure remains stable and flexible even in high-heat environments where other materials would degrade, harden, or melt.
To be used in gasketing applications, raw silicone must be vulcanized or expanded into a polymeric form, like foam, sponge, or solid rubber. Each of these materials serves different roles depending on the needs of the application.
What Is Silicone Foam?
Silicone foam is created through a chemical reaction that produces a low-density, closed-cell or semi-closed-cell structure. It starts as a liquid silicone that is expanded with blowing agents and then cured, resulting in a soft, lightweight, and compressible material.
Silicone foam is known for its exceptionally low density (from 12–28 lbs./ft2), high flexibility, and excellent thermal and environmental resistance. It is ideal for applications that require gentle sealing, vibration isolation, and insulation in outdoor environments exposed to high temperatures, UV light, or flame. These types of gaskets can be used in high temperature applications or seals in food processing (meets FDA 21 CFR 177.2600).
Silicone foam is softer than silicone sponge, allowing liquid to pass through. When compressed, it can form a tight seal that blocks water and can resist weathering.
Why Use Silicone Foam?
Thermal stability resists temperatures between -60 and 401-degrees Fahrenheit, depending on the grade
Lightweight and low density makes it ideal for applications where weight is a concern
Conformable and compresses more easily than silicone sponge to fill gaps and irregular surfaces
Resilient and maintains shape after compression (low compression set with a UL50/UL50E compression rating)
Flame resistance is available in UL 94 V-0 certified grades
Shock and vibration absorption makes it useful in electronics, aerospace, and transportation
Weather and UV resistant, so it’s excellent for outdoor and high-UV exposure applications
Like all silicones gasketing materials, these foams can be used for indirect food contact applications
BISCO® Silicone Foam and Alternatives
One of the most widely used brands of silicone foam materials is BISCO®. Their materials are available in soft (BF-1000 and BF-2000), medium (HT-800), and firm (HT-820 and HT-840) grades and are used widely in transportation, electronics, and appliance manufacturing due to their tested consistency and UL recognition.
There are also silicone foam alternatives that offer comparable performance at a potentially lower cost. These materials, mirror many of the same characteristics and are often drop-in replacements depending on the application and performance requirements.
What Is Silicone Sponge?
Silicone sponge is also created from liquid gum type silicone, but it typically has a more uniform closed-cell structure than silicone foam. It is produced using a chemical blowing process or an extrusion and curing method. The resulting material is denser than foam, offers more consistent sealing, and provides a balance between softness and mechanical integrity.
As closed-cell foams, silicone sponge comes in higher densities (that range from 21–43 lbs./ft2), allowing them to be used in gasketing applications where there is a need for both compression and durability, especially where a moderate sealing force is applied. Despite its name, the material does not absorb water; it’s naturally waterproof. 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.
Why Use Silicone Sponge?
Excellent sealing under low compression force
Higher tensile and tear resistance than silicone foam (up to 130 psi)
Good rebound and compression set resistance
Wide range of densities and firmness levels available
Can be flame-rated to meet MIL-R-6310 Type II specification and UL 94V-0
More durable than foam in dynamic applications
Operate at higher temperatures than silicone foam (generally between -100 and 500-degrees Fahrenheit).
Resistant to water, ozone, chemicals, and UV light
One of the most resilient closed cell foams with low compression set values
Like all silicones gasketing materials, these foams can be used for indirect food contact applications
A Closer Look at Sponge Options
Manufacturers like Saint-Gobain offer their own high-performance sponge materials. Products like the Saint-Gobain Norseal Series provide excellent flame resistance, low compression set, and compliance with standards like MIL-R-6130 and ASTM D6576.
These sponge materials come in various durometers, thicknesses, and adhesive-backed formats, making them highly customizable for sealing enclosures, protecting against vibration, or managing heat.
What Is Solid Silicone Rubber?
Solid silicone rubber is a non-foam, fully dense elastomer created by molding or extrusion. It’s a flexible high temperature vulcanized rubber that has long polymer chains and a high molecular weight. Unlike foam and sponge, it does not contain internal gas pockets. Solid silicone is used in gasketing applications where high sealing force, durability, and resistance to mechanical stress are needed. 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).
Common forms include compression-molded sheets, extruded profiles, or die-cut parts. Solid silicone can be reinforced with fiberglass, colored for identification, and manufactured in FDA- or UL-compliant grades. The material can also be fabricated and sterilized for food contact safe rubber protectors (meets FDA 21 CFR 177.2600), oven seals, etc.
Why Use Solid Silicone Rubber?
High mechanical strength makes it ideal for dynamic sealing, compression loads, and precision fit
Extreme temperature resistance is between silicone sponge and foam (between -80 and 500-degrees Fahrenheit)
Excellent tear and abrasion resistance
Low compression set for long-term sealing
Chemical, UV, ozone, and solvent resistance
UL 94 V-0 and FDA-grade options available
Durable against high cycling and environmental exposure
Can also be used for electrical insulation
Different Types of Silicone Rubber
Solid silicone rubber comes in several formulations to meet application-specific needs:
General Purpose Silicone: good balance of strength and flexibility for industrial use
High-Temperature Grades: formulated to resist continuous exposure above 260°C
FDA-Compliant Silicone: safe for use in food and beverage applications
Conductive Silicone: filled with conductive particles for EMI/RFI shielding
Fluorosilicone: resistant to fuels, oils, and aggressive chemicals
Each type offers trade-offs in flexibility, chemical resistance, and thermal range, so it’s important to match the formulation to the environment.
The Ideal Applications for Silicone Foam, Sponge, and Solid Rubber
Silicone Foam
Lightweight seals in aerospace and avionics
Gasketing in battery packs and enclosures
Gap filling around displays, lighting, or panels
Low-pressure door seals in appliances or electronics
Silicone Sponge
HVAC system gaskets
Vehicle door seals and enclosure seals
LED lighting enclosure protection
Outdoor signage and display gaskets
Cushioning or vibration dampening in machinery
Solid Silicone Rubber
High compression sealing in engines or motors
Valve or pump gaskets
High-temperature oven or appliance door seals
Sanitary gaskets in medical or food-grade equipment
EMI shielding when combined with conductive fillers
How to Choose the Right Silicone Gasket Material
Choosing between silicone foam, sponge, and solid rubber comes down to understanding your application’s unique demands:
Temperature Range: all three materials resist heat well, but solid silicone is best for extreme conditions.
Compression Force: foam works with very low force; sponge balances softness and strength; solid is for high-compression seals.
Environmental Resistance: all silicone types resist UV, ozone, and moisture, but fluorosilicone and specialized sponge grades offer enhanced chemical protection.
Sealing Pressure: foam fills gaps; sponge creates uniform seals; solid ensures tight, precision seals.
Insulation: silicone foam has the best K factor for insulation with 0.63 BTU in/hr/ft²/°F
Fluid seals: typically, silicone sponge will provide the optimum balance of compression and watertight seals, though softer solid silicone rubbers, and highly compressed silicone foams may be the right fit in some applications.
Durability Needs: solid silicone offers the highest resistance to wear, while foam and sponge are better for cushioning and vibration absorption. Silicone sponge does offer good wear resistance.
Electrical insulation: solid silicone rubber will give you the best electrical insulation properties.
Looking for Silicone Gaskets? We Can Help
At Engineered Materials, we guide customers through this selection process by evaluating environmental, mechanical, and regulatory requirements. Whether you need custom die-cut parts, PSA-backed gaskets, or support during prototyping, we have the materials and converting expertise to match.
If you’re unsure which type of silicone gasket material is right for your design, contact us today. Our team can help you compare options, choose the best solution for your application, and deliver parts customized to your specs.