Foam sponge rubber stands out as a uniquely adaptable and valuable material. Foam sponge rubber, a type of cellular rubber, possesses distinct properties compared to solid rubber. Unlike solid rubbers, sponge rubber excels in applications requiring superior compression and flexibility. Its primary characteristic, compressibility, makes it ideal for applications prioritizing cushioning and surface flexibility over rigidity. For example, closed cell rubber can provide a reliable seal for uneven surfaces where solid rubber lacks the compressibility to do so. Similarly, open cell rubber offers superior shock absorption and flexibility in cushioning in places traditional rolled rubber cannot provide as they are too rigid.

Sponge rubber products are available in two variations: open cell and closed cell. Open cell structure allows air and fluids to pass through, making the material breathable and useful for cushioning. In contrast, closed-cell rubber exhibits a more rigid and dense structure. Its outer layer lacks interconnected pores, forming a barrier against water and air. This impermeability makes it an excellent choice for insulation. Recognizing the distinct properties of each cell structure, foam sponge rubber is manufactured from a variety of elastomers, such as neoprene, EPDM, and other blends. When combined with the chosen cell structure, these elastomers offer unique characteristics that cater to particular uses. Foam sponge rubber is typically produced from neoprene sponge, sponge EPDM, or blends of rubber compounds. Surprisingly, this versatile rubber sheet, now indispensable in modern industry, was born from an accidental breakthrough. Here is how it was discovered.

Brief History of Foam Sponge Rubber

In 1937, German chemist Otto Bayer made an accidental breakthrough while experimenting with synthetic polymer materials. During World War II, with international supply chains disrupted and Japan controlling much of Southeast Asia’s rubber production, Germany faced mounting demand from the chemical and industrial sectors for cheaper alternatives with performance attributes comparable to natural rubber. The wartime shortages of raw materials accelerated the search for synthetic substitutes that could meet the demands of emerging technologies in insulation, adhesives, cushioning, and coatings.

Driven by the urgent need for synthetic rubber alternatives during World War II, German scientists, including Otto Bayer and his co-workers, intensified their research into new polymer materials. Bayer’s work during his time at IG Farben in Leverkusen, Germany, involved mixing small quantities of chemical compounds to experiment with a technique called polyaddition, which involved altering the molecular structure of compounds. One of these experiments, using a family of chemical building blocks called diisocyanates, unexpectedly formed a foam-like material. The starting products for the foam were mixed in a waste bin in the laboratory, triggering a chemical reaction. Although his closest colleagues were at first skeptical of his principle of polyaddition using diisocyanates, this accidental synthesization of the first polyurethane foam would eventually be Otto Bayer’s most significant contribution to rubber chemistry. He and his team patented the chemistry of polyurethanes in 1937, and it would be another 10 years before his invention could be developed into the customized materials we use today. People most commonly recognize polyurethanes as flexible foams used in furniture cushioning, mattresses, earplugs, chemical-resistant coatings, specialized adhesives and sealants, and packaging materials.

Initially, the foam sponge rubber Bayer developed was made of neoprene, as it was one of the first widely available synthetic rubbers. However, foam rubber materials are available in various compounds, including neoprene, EPDM, and blended formulations.

Closed Cell Rubber – Blend – 39″ x 78″ – Adhesive Backed

• Temperature Range: -40 F to +200 F
• Durometer rating of 20-25 Shore C
• Sheets available in size of 39in by 78in
• Ideal for use in shock absorption and gasket related applications

Moderate Weather Resistance: The closed cell blend inherits a good level of weather resistance from its combination of neoprene SBR. Each of these rubber types are made to withstand inclement weather and associated effects. This means that it can handle a moderate level of ozone, UV rays, moisture and more. Using this combination allows the sponge rubber to be employed in outdoor applications.

A Durable Sponge Rubber: As a direct benefit from the SBR rubber used to make it, this closed cell sponge rubber possesses a good degree of physical durability. SBR is popular for use in vehicle tires because it is known for its superior physical strength and resistance to abrasions. This allows tires to handle the roughest road conditions. Using SBR in closed cell blend gives it a higher level of physical abrasion resistance.

How Do They Make Foam Rubber?

Elastomeric foam is created through a chemical reaction between diisocyanates and polyols. Both of these primary ingredients are typically derived from crude oil, although polyols can also be made from natural oils sourced from renewable materials such as vegetable oils. The production of foam rubber is largely dependent on the petroleum industry. The production process begins by mixing these two compounds, which triggers a reaction that causes them to form a polymer structure. The diisocyanates contain two reactive isocyanate groups that bond with the hydroxyl groups present in the polyols. The reaction leads to the formation of a network, resulting in the formation of a foam structure. The final properties of the rubber foam, such as density, flexibility, and rigidity, can be controlled by adjusting the ratios of diisocyanates to polyols and incorporating other additives, such as blowing agents, which help create the foam rubber’s cellular structure.

Foam rubber sheets are created when you combine liquid polymers, such as polyols and polyisocyanates, with a blowing agent, such as Dinitrosopentamethylene tetramine (DNPT) and toluene diisocyanate (TDI). The selected blowing agent generates the gas bubbles inside the liquid plastic mixture of diisocyante, creating the unique foam structure in those rubber sheets. The resulting foam sponge rubber is soft and flexible, thanks to the tiny air pockets formed during the process. Foam sponge rubber is a highly compressible product compared to solid rubber and is, therefore, a good choice for cushioning, sealing, or insulating applications.

How the foam rubber should be made varies depending on the final properties and uses it will serve. For example, some of the varied properties of foam sponge rubber include the molecular structure of its liquid polymers and blowing agent, the quantities used, and their unique reaction temperature.

Liquid Polymers Proportions: Polyols are monomers containing at least two active hydrogen atoms. They are usually made from polyesters, polyethers, or hydrocarbons. The type of polyol chosen determines whether the foam is flexible or rigid. When polyols are mixed with isocyanates, they quickly react with each other, allowing the polymerization to happen.

Blowing Agent Proportions: The amount of blowing agent used affects the density of the foam. Higher levels of blowing agents mean water levels and foam stabilizers must be adjusted to keep uniformity in bubble size and foam formation.

Density and Compressibility: Foam density is critical in determining its stability and flexibility. High-density foam has more firmness and stability and is suitable for heavy-duty applications such as automotive seals; on the contrary, low-density foam is softer and better suited for lightweight cushioning materials such as those used in packaging.

Typically, manufacturers have preset measurements for the chemical reactions they want to perform on their metered pumps. The metered pumps release specific amounts of each chemical into the mixing head, where chemicals are blended. Once the foam is formed, it can be cut into various shapes and sizes, offering ample flexibility.

Matching foam density to the material type ensures the final product meets the intended performance. Whether neoprene is used for thermal resistance or EPDM is used for durability. For example, Sponge EPDM rolls of rubber are used for their weather and chemical-resistant properties.

Closed Cell Rubber – EPDM – 39″ x 78″

Closed Cell Rubber – EPDM – 39″ x 78″

• Temperature Range: -40° F to 200° F
• Durometer rating of 15 Shore C
• Sheets available in size of 39″ by 78”
• Perfect for use in indoor or outdoor applications

High Compressive Strength: Closed cell rubber is a bit different from its open cell counterpart in terms of compressive strength. While open cell sponge rubber can rebound back to its original shape very quickly, closed foam rubber sponge takes a bit longer to do so. This allows the closed cell EPDM sponge rubber to handle high- pressure applications at a better rate, making it more durable.

Perfect for the Outdoors: The excellent ability of this closed cell rubber to operate in the outdoors is all thanks to the compound of EPDM rubber in its structural makeup. It has an excellent level of resistant to both UV rays and ozone. Outdoor factors like UV and ozone may not damage a material immediately, but they can definitely degrade a material over time. The EPDM compound in this sponge rubber allows it to remain exposed to the elements for extended periods of time. This is the primary reason why EPDM material is a popular elastomer to use in applications such as window sealing on vehicles and homes.

Open Cell EPDM vs Closed Cell EPDM

Properties of Foam Sponge Rubber

Foam sponge rubber is a lightweight, porous material characterized by its cellular structure, which can be open-celled (with interconnected pores) or closed-celled (with sealed cells). This structure, along with the chosen elastomer (like neoprene or EPDM), determines its key properties:

• Compressibility and flexibility: Allows easy deformation and return to its original shape.
• Insulation: Provides thermal and acoustic insulation and resistance to water and air (closed-cell).
• Lightweight and durable: Offers a balance of strength and weight.

These characteristics make it an efficient gasket, padding, or insulation against moisture, air, and debris. Its cellular structure plays a pivotal role in its performance, with open-cell and closed-cell variations offering distinct advantages. This diversity allows foam sponge rubber to excel in a variety of settings. To explore these capabilities further, let’s dive into the differences between cellular rubber types.

What is Cellular Rubber?

Cellular rubber, or foam rubber, differs significantly from solid rubber due to its unique structure containing air pockets, either open or closed. These air pockets provide cellular rubber with greater flexibility and compressibility, making it more adaptable. In contrast, solid rubber is denser and more rigid, lacking the compressible nature of cellular rubber. At the same time, solid rubber excels in applications requiring durability and rigidity, and cellular rubber’s lower density and ability to return to its original shape after compression make it ideal for seals, gaskets, and thermal insulation. Furthermore, the air-trapping ability of cellular rubber enhances its function as an effective thermal insulator, whereas solid rubber is less efficient due to its higher density.

Its cushioning properties make it ideal for protective packaging, medical equipment, and sports gear, where impact absorption is essential. Additionally, its lightweight and flexible nature allows it to be used in automotive components to reduce noise, vibration, and harshness while minimizing weight. We offer a wide range of foam rubber sheets made from various elastomers, ensuring a good fit to meet any customer’s specific needs in materials and purposes. Our sponge rubber products are made out of EPDM, neoprene, and blends of various rubber types. The different rubber materials are chosen based on their unique chemical and physical properties, making them suitable for other applications. For instance, a neoprene sponge rubber sheet is known for its strong resistance to oil, grease, and chemicals, making it perfect for applications where exposure to such substances is daily. On the other hand, EPDM sponge rubber sheeting is exceptionally durable in outdoor environments, as it offers excellent resistance to UV rays, moisture, and ozone. When these elastomers are used to create cellular rubber, the resulting compound inherits these properties.

We also offer Closed Cell Rubber – Blend, a blend of SBR rubber and neoprene. Neoprene provides moderate UV and ozone resilience, making it suitable for outdoor applications. SBR enhances its physical durability, allowing it to withstand moderate abrasions, though it remains softer than solid rubber. Neoprene content also provides light oil resistance, making it practical for limited oil exposure, though it is not ideal for heavy oil contact.

Closed Cell Rubber – Blend – 39″ x 78″

• Temperature Range: -40 F to +200 F
• Durometer rating of 20-25 Shore C
• Sheets available in size of 39in by 78in
• Ideal for use in shock absorption and gasket related applications
• A versatile blend of closed cell sponge available at affordable rates

Moderate Weather Resistance: This closed cell sponge rubber benefits from the presence of Neoprene material since each sponge sheet is composed of Neoprene and SBR. A characteristic of Neoprene rubber is its good resistance to outdoor weathering effects such as UV rays and ozone. As a result, it is often employed wherever a rubber part is needed for the outdoors. This blended cellular rubber possesses a moderate degree of outdoor weather resistance.

A Durable Sponge Rubber: As a direct benefit from the SBR rubber used to make it, this closed cell sponge rubber possesses a good degree of physical durability. SBR is known for its superior physical strength and resistance to physical abrasions. It is the reason why SBR is so popular for use in vehicle tires, which are expected to endure harsh physical conditions on a daily basis. Although cellular rubber tends to be a softer material overall, especially when compared to its regular solid rubber counterparts, it is still durable enough to handle some moderate level physical abrasions.

Closed Cell Rubber

Closed cell rubber has a denser and more uniform structure than open cell rubber. Each of its cells does not connect, giving it a closed structure fundamentally different from the visible air pocket characteristics of open cell rubber. This insulated structure makes closed cell foam suitable for applications requiring water resistance and insulation. For instance, a version of it is often used as a moisture barrier and insulation against water. In addition to being water-resistant, closed cell foam rebounds slower than open cell types. It is well suited for applications that demand more excellent sturdiness and durability, making it perfect for shock absorption and gasket-related operations. Its high density also contributes to better overall strength, making it a popular choice in operations requiring heavy-duty performance.

To better understand the uses of closed cell foam sponges, looking at three types: Neoprene, EPDM, and SBR foam is helpful. Neoprene foam is highly resistant to weather and chemicals, staying flexible and durable in harsh conditions. It’s used in the automotive, aerospace, and electronics industries for seals, gaskets, and insulation. EPDM foam offers strong resistance to UV rays, ozone, and extreme weather, making it perfect for outdoor use. It’s commonly used in construction, automotive, and HVAC industries for seals, gaskets, and insulation. SBR foam is a low-cost material known for its good resilience and moderate resistance to the weather. It is utilized within manufacturing, automotive, and construction for sealing, cushioning, and vibration damping. Each type of closed cell foam has its unique advantages, helping provide durability, flexibility, and insulation across different industries.

Variants like SBR are used for general purposes, while closed cell neoprene offers moderate oil resistance and is commonly used in automotive and industrial settings. Closed cell EPDM is particularly valued for its outdoor performance, as it prevents water penetration and retains moisture on its surface. With a durometer range of 15 to 25 Shore C, closed-cell rubber is softer than solid rubber, allowing for greater flexibility and compression, making it perfect for sealing and gasketing tasks while maintaining durability under pressure.

Closed Cell PE – White – 39″ x 78″

• Cellular structure provides high compressibility
• Operating temperature range: -110° F to 190° F
• Can be rolled up for easy transport and storage purposes
• Pressure sensitive adhesive backing available upon request

High Compression: Closed cell sponge is the best choice of material whenever the need for compressibility arises. The cellular composition of Closed Cell PE is made up of a multitude of tiny air pockets that give the whole sheet a more pliable nature. When pressure is applied to these air pockets, they close in and thus allow for compression. For example, if you take an object like the tip of a pen and press down onto the sheet surface, you will find that the pen will sink in to a significant degree. When you remove that pen, the sheet will slowly revert back to its original form. This is due to the fact that the air pockets bounce back to their original form once the source of the pressure is removed.

Non-Marking Material: The Closed Cell PE sheet is a crisp shade of white. This is a great color for the aesthetic needs of specific applications, such as protective padding for boxes carrying sensitive electronic equipment or bottles. More important is the fact that white colored polyethylene sponge sheets will never leave any marks or stains on the surfaces they come into contact with.

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Open Cell Rubber

On the contrary, open cell rubber is more porous in structure and has visible air pockets that are interconnected with its neighbouring cells, creating an open network throughout the material. Because of this, it has a better compression ratio, meaning that the material is bounced back to its original shape faster than closed cell rubber. However, because of its porosity, open cell sponge rubber is more susceptible to liquid absorption, which makes it ideal for applications where moisture can pass through the material, such as filtration or soundproofing.

Our Open Cell Rubber – EPDM is an ideal choice for outdoor applications due to its excellent UV and ozone resistance, making it durable in prolonged exposure to the elements. Its soft, compressible nature allows for flexibility and high compressibility, making it perfect for what kind of seals, gaskets, and protective padding need constant pressure. Open cell EPDM’s cellular structure compresses easily under pressure and recovers quickly once the pressure is removed. This ensures long-term performance in applications that require constant pressure.

Open and closed cell rubber serve essential roles in various industries, each offering unique benefits based on the specific application needs. Open-cell rubber is more flexible and compressible, making it ideal for uses that need moisture passage and the ability to withstand pressure. In contrast, closed-cell rubber is denser and more moisture-resistant, making it better suited for insulation and sealing tasks. At Rubber-Cal, we provide a wide selection of foam sponge rubber options, including neoprene, EPDM, and SBR blends, to ensure you can find the ideal material for your project.

Open Cell Rubber – EPDM – 39″ x 78″

• Operating temperature range from -40° F to 160° F
• Easy to roll up for transportation and storage purposes

Made for the Outdoors: Open cell EPDM is the perfect foam sheet for any application where the presence of sunlight and other elements is present. UV and ozone have a tendency to harm certain types of materials after a while, but that is not the case with EPDM foam. It is designed to have a longer lifespan when exposed to the elements.

Excellent Compressibility: This EPDM rubber foam is among the most compressible products currently available. The cellular composition of this open cell rubber material is the secret behind its ability to compress. The cell structure is composed of tiny air pockets that have gaps in between them. When force is applied to the surface of the EPDM sponge, these air pockets will close in on themselves. The source of the pressure will also not face any resistance due to the soft nature of open cell sponge. The EPDM foam sheet will maintain its compressed form as long as the object applying the pressure remains.

Fast Recovery: The open cell EPDM has the ability to revert back to its original shape after compression. When the source of pressure is removed from the open cell rubber sheet’s surface, the air pockets within its cellular composition will revert back to their original shape. This helps the EPDM rubber foam maintain a working lifespan suitable to long-term use in applications that require constant compression.

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Is Sponge Rubber Waterproof?

Foam sponge rubber is not entirely waterproof but can resist water, depending on its type and structure. Both open and closed cell rubber offer some level of waterproofing. However, their effectiveness in such applications varies significantly. Thanks to its nonporous structure, closed cell rubber is highly water-resistant. The absence of visible air pockets means closed cell rubber sheeting does not allow liquids to pass through. This makes them an excellent choice for applications where water exposure is daily, such as seals, gaskets, and wetsuits. This type of rubber is also ideal for outdoor applications, where water resistance is crucial. Closed cell rubber materials like Closed Cell Rubber – EPDM do not absorb fluids or moisture readily due to their unique structure. The cells are sealed off, preventing water and other liquids from quickly penetrating. Instead, moisture tends to remain on the surface for an extended period, making wiping water droplets easier.

Like its closed cell counterpart, open cell sponge rubber is designed for compression and flexibility, but its structure differs slightly. It features an interconnected network of cells that creates a porous structure, allowing it to absorb moisture and water. This makes it ideal for applications where moisture retention or absorption is needed. The material is permeable, which means air, liquid, and gases can easily pass through it. This property is well-suited for uses where moisture uptake or cushioning is required, such as in padding, insulation, or soundproofing. Retaining moisture also benefits applications like filtration and sealing in environments where liquid absorption is essential.

So, does foam rubber absorb water? The answer is whether the foam is in open or closed cell rubber. Open cell rubber is specifically designed to absorb moisture and water. On the other hand, closed cell rubber does not absorb water due to its nonporous structure.