Foam rubber is similar to sponge rubber, but that doesn’t mean foam rubber gaskets and sponge rubber gaskets are the same. Learn about the intricacies of compound selection, and what buyers and designers need to know about open-cell and closed-cell elastomers.

Foam rubber can be soft like sponge rubber, but that doesn’t mean these two types of elastomers are the same. From chemical additives to curing systems, foam rubber is different than sponge rubber. For technical buyers and design engineers, understanding these differences is an important part of compound selection. Gasket designers also need to understand that there are differences between material types such as polyurethane foams and silicone foams, and that foam rubbers can come in multiple grades.

How Foam Rubber Is Made

Foam rubber materials are produced with a blowing agent that creates a mass of small bubbles in a liquid mixture. Depending on the specific foam rubber compound, this mixture can contain chemicals or additives such as colorants and flame retardants. For example, some UL94 gaskets are made of flame-resistant foam rubbers such as silicone or polyurethane compounds. These silicone and polyurethane elastomers also provide different degrees of environmental resistance, such as to UV rays.

How Sponge Rubber Is Made

Sponge rubber materials are also made with a gas, but the nitrogen that’s used in sponge rubber doesn’t produce a foam like the blowing agents used in foam rubber. Foaming is a specific production process, and material properties vary accordingly. Like foam rubber, however, sponge rubber offers both cushioning and insulation. All foam rubbers aren’t soft (rigid foams are used in structural applications), but both foam rubber and sponge rubber have either an open-cell or a closed-cell structure.

Open Cell Rubber vs. Closed Cell Rubbers

Open-cell rubber contains interconnected pockets that permit the passage of air, water, and other chemicals when the elastomer is not compressed. Closed-cell rubber contains balloon-like cells that are filled with gas and 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. The specific type of compound, such as a silicone or urethane, also imparts particular properties.

Polyurethane Foam Rubber Gaskets

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

Silicone Foam Rubber Gaskets

Custom gaskets made of silicone foams are available in soft, medium, firm, and extra-from grades for specific amounts of compressibility. Silicone foam rubber has a lower compression set than sponge silicone rubber, and offers better flame resistance. Because of silicone rubber’s temperature stability, all of these elastomers are great for high-temperature gaskets and low-temperature gaskets. Non-toxic, chemically-inert silicones are also a good choice for sanitary applications.

Pick a Partner – Then a Material

The process of picking the right foam rubber or sponge rubber can be complex? Have you considered starting your search by picking the right partner instead? Elasto Proxy works with a trusted network of material suppliers, and has the application knowledge and technical expertise to help you with compound selection. With our custom fabrication expertise, we can then create specialty gaskets that meet all of your application requirements.

How can we help you? Learn more about us by downloading our Compound Selection e-book.

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