Foam rubber gaskets can be soft like sponge rubber gaskets, but that doesn’t mean foam rubber and sponge rubber are the same. From chemical additives to curing systems, foam rubber is different. Plus, foam rubber isn’t always soft. In fact, rigid foams are used in some structural applications. Yet, both foam rubber and sponge rubber can have either open cells or closed cells.

Gasket designers also need to consider two key foam rubber properties, compression set and stress relaxation, that sponge rubber materials share. In addition, the type of rubber material affects sealing and insulation. There’s a lot to consider during gasket design, which is why it’s important to choose a fabricator who can answer questions like the ones you’ll read about below.

How are foam rubber gaskets made?

Foam rubber is produced with a blowing agent that creates a mass of small bubbles in a liquid mixture. Depending on the specific compound, this mixture can contain chemicals or additives such as colorants, bactericides, fungicides, or flame retardants. Foam rubber is supplied as sheets, rolls, and extrusions, and these stock materials can be waterjet cut into foam rubber gaskets.

How are sponge rubber gaskets made?

Sponge rubber is also made with a gas, but the nitrogen that’s released doesn’t produce a foam like the blowing agents used in foam materials. Like foam rubber, however, sponge rubber comes in different compounds, each with specific material properties. Sponge rubber is supplied as sheets, rolls, and extrusions, and these stock materials can be waterjet cut into sponge rubber gaskets.

water jet cutting
Water Jet Cutting at Elasto Proxy

What’s the difference between open cell and closed cell materials?

Foam rubber and sponge rubber have a cellular structure with either open cells or closed cells.

  • Open-cell rubber contains open, interconnected pockets that permit the passage of air, water, and other chemicals when the material is not compressed.
  • Closed-cell rubber contains balloon-like cells that hold nitrogen gas and thus prevent the passage of these substances at low pressures.

Typically, application requirements and environmental conditions determine whether you need open cell or closed cell rubber. Specific compounds include polyurethane, polystyrene, silicone and EPDM rubber. 

Elasto Proxy offers a sponge sample kit

How are polyurethane foam rubber gaskets used?

Polyurethane foams are used for vibration control and shock absorption. They provide increased energy absorption with increased density, predictable performance under compressive force, and low permanent deformation under constant resistance. Polyurethane foams won’t become wider when compressed, which makes them a good choice when space is tight. Applications include hood gaskets in mobile equipment, shock absorbers for industrial machinery, and vibration isolators for appliances.

Open-cell polyurethane foams are used in medical and electronic packaging applications. For example, polyurethane foams are used in healthcare facilities and laboratories because these gasket materials can be compounded with additives such as bactericides and fungicides. Open-cell polyurethane foam is also used in prosthetic devices and medical filters. Because they provide outstanding cushioning, polyurethane foams are also used to protect electronic devices.

How are polystyrene foam rubber gaskets used?

Polystyrene foams are rigid, structural materials that are strong, lightweight and moisture resistant. They help reduce product weight and have a high stiffness-to-weight ratio. Other types of structural foams have a sandwich-like structure with a foam core between two thin but solid layers. Reticulated foams are used for filters and can be compounded with bactericides, fungicides and other additives. Foam rubber that is fabricated into elastomeric pads can be attached to vacuum tooling for manufacturing.

Rubber profiles from Elasto Proxy

How are silicone foam rubber gaskets used?

Custom gaskets made of silicone foam are available in soft, medium, firm, and extra-firm grades for specific amounts of compressibility. Silicone foam rubber has a lower compression set than silicone sponge and offers better flame resistance. Because of silicone’s temperature stability and non-toxic properties, it’s a good choice for the foam gaskets used in sanitary applications.

How are sponge rubber gaskets used?

Sponge rubber gaskets that are made of neoprene, EPDM, nitrile, or silicone rubber are used for shock absorption and provide good compression and recovery. Sponge rubber is also used in bulb seals for doors, hatches, and enclosures. These rubber profiles have separate bulb and retainer sections and are made of different materials. Typically, the bulb portion is made of an EPDM sponge.

FDA approved silicone sponge rubber may be required for food contact or medical applications. There’s a difference between FDA approved and FDA compliant materials, however, so it’s important to choose compounds carefully. Elasto Proxy can help you with this process and can provide advice about whether your need foam rubber gaskets or sponge rubber gaskets for your application. We keep hundreds of profiles in stock and offer waterjet cutting for toolless gasket fabrication.