Foam Rubber Sheet vs. Sponge Rubber Sheet: What’s the Difference?

Foam rubber sheet and sponge rubber sheet are two distinct materials that are often confused with each other. Both foam and sponge sheets are rubbery materials composed of elastomers, and synthetic polymers with elastic properties. More than elasticity, however, elastomers are deformable as well. In other words, they can be compressed, bent, or stretched, and then returned to their original resting shape without being damaged or permanently deformed. However, in terms of composition, method of formation, and applications, foam and rubber sheets are very much different.

How Foam and Sponge Rubbers Are Made: Similarities and Differences

The cell structure of both foam rubber sheets and sponge rubber sheets consists of thousands upon thousands of interconnected, bubble-like cells formed by introducing gas or chemicals directly into a polymeric compound while in its liquid state. As the polymer cools and hardens, depending on the process, bubbles form into either open-cell or closed-cell units, meaning that the cells can either hold air or permit its passage. 

More specifically, foam rubber is produced by dissolving a chemical or gas agent with a blowing agent to generate gas bubbles in a liquid polymer mixture. The liquid mixture for foam rubber includes liquid polymers (Polyols, Polyisocyanates), water, and colorants. The composition of the liquid polymers and the type of gases determines how flexible or rigid the foam rubber will be. Carbon dioxide gas is used to make the foam flexible, whereas hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs) gases are used to form a more rigid foam rubber. Foam materials are manufactured from polymers such as polyurethane, polyethylene, EPDM rubber, silicone, PVC/Nitrile, Neoprene sheet, and acrylic, among others. 

Sponge rubbers, in general, are made with such elastomeric compounds as silicone, neoprene, EPDM, nitrile, and other materials. Like foam rubber, the cellular structure of sponge rubber contains interconnected, bubble-like cells that are either open-cell or closed-cell. Open-cell material allows air, water, and other chemicals to pass through. The open cell structure is formed by adding sodium bicarbonate into a heated mold with other ingredients. The reaction creates bubbles and releases carbon dioxide gas, causing the material to expand and create voids, resulting in a sponge-like material substance with a porous structure. Elastomers used for open-cell sponge profiles include polyurethane, polyester, and polyether.

Closed-cell sponge rubber does not allow the passage of gas or liquid, which, consequently, makes the material denser. The closed cells are formed by adding a chemical powder that decomposes when heated, producing nitrogen gas that fills the cells and gives the material the needed strength and density. Sponge rubber can be manufactured with different densities, from soft to medium or firm. The range of elastomeric compounds for closed-cell sponge rubber includes EPT, EVA, nitrile rubber, silicone, Neoprene, EPDM, PVC sponge, and SBR sponge. Polyethylene and polyurethane are also used in applications.

Sponge and Foam Rubber Sheet Applications

With numerous performance characteristics, foam and sponge rubber components offer consumers a broad range of applications. A foam rubber, for example, can be flexible, rigid, or reticulated depending on the application requirements. Flexible foams are derived from polyurethane for shock absorption and vibration control. Major applications include shock absorbers for industrial machinery, hood gaskets in mobile devices, and vibration isolators for appliances.

Rigid foams are manufactured with polystyrene and are strong, light, and moisture-resistant, with a high stiffness-to-weight ratio. Common applications include filters treated with bactericides or fungicides and are a preferred choice for insulation, packaging, surfboards, and automobile components.

Reticulated foams are an extremely porous, open, net-like foams useful for filtration. Some common applications include filters for small combustible engines like lawnmowers, face masks, vacuum cleaners, air compressors, and electrical equipment.

Applications for open and closed sponge rubber sheets are numerous and widely used throughout many industries such as automotive, aerospace, food, and beverage packaging, medical packaging, marine, public transport, chemical, and electronics. Common uses for open-cell sponge rubber components are used for gaskets, seals, and protective padding due to their resistance to sunlight and UV rays. Closed-cell sponge rubber components are commonly used for cushioning, soundproofing, weather-stripping, shock absorption, vibration dampening, and thermal insulation.

Contact the Experts at Manufacturer’s Rubber & Supply 

Unsure of which rubber sheet products your application requires? Manufacturer’s Rubber & Supply will help ensure you select the right material for your manufacturing, building, or other industrial applications. We are a single-source supplier that can meet all your rubber application needs. Contact us today for more information or to speak with one of our experts to answer any questions you may have.

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