Foam Rubber vs. Sponge Rubber: Know the Difference

Many people find it difficult to differentiate between foam rubber and sponge rubber. Looking at the two materials, you may assume they are the same.

However, there are fundamental differences – ranging from manufacturing process, properties and applications.

Let’s take a look at the two:

What is Foam Rubber?

Foam rubber has a light and soft texture thanks to its air-filled structure. It’s made using a “blowing agent,” usually a gas that expands and creates bubbles during production.

You can use common blowing agents are carbon dioxide for flexibility or hydrochlorofluorocarbon for rigidity.

Foam Rubber
Foam Rubber

What is Sponge Rubber?

Sponge rubber similarly contains numerous tiny air pockets molded within, although these manifest in two primary forms. For the open-cell type, the pockets are interconnected to allow easy passage of both air and liquid components.

Closed-cell keeps each bubble sealed off for better liquid-blocking. Both varieties absorb shocks and pressure well.

Sponge Rubber
Sponge Rubber

Material Composition

· What Foam Rubber is made of

Foam rubber is made from synthetic polymers combined with gases during production. Common resins include polyurethane and latex which give foam rubber its soft, flexible qualities.

· What Sponge Rubber is made of

Sponge rubber on the other hand contains natural or synthetic rubber compounds and sometimes a blend of both. Silicone spongecontains polydimethylsiloxane cured with heat to form its shape. Both provide compliant, durable materials.

Silicone Sponge
Silicone Sponge

Manufacturing Process

· Foam Rubber

First, you will start the production process by carefully preparing the proper liquid mixture in large vats. Polyols, which provide structure and flexibility, get blended with polyisocyanates for cross-linking. Water and additional compounds are added to initiate the reaction.

Next comes the blowing agent. Carbon dioxide is a common choice. You can add it as a liquefied gas or through a chemical reaction. Its amount must be precisely measured, as too much could make the foam too lightweight and brittle.

With ingredients uniformly combined, heat gets applied to accelerate the chemical process. Within moments, the mixture blooms into a sprawling froth as countless CO2 bubbles inflate throughout.

The foam then journeys through an oven where it doubles, triples or more in size. Inside, branching polymer chains weave between each bubble, setting the structure like a solidifying web. Quality checks monitor heat application to ensure consistent properties.

After cooling, you will then cut the foam, press or otherwise trimmed into usable parts. Depending on your specific requirements, you can customize it by adding colorants, antimicrobial or fire retardants. The finished product emerges resilient yet tender – ready to cushion whatever objects require protection.

· Sponge Rubber

For sponge rubbers, production follows a simpler path.

You can choose either natural or synthetic rubber alongside the needed additives and cure accelerators.

As with foam rubber, you will use to activate the chemical reaction. But instead of involving a blowing agent, the rubber mass itself swells open like a sponge soaking up water. Microscopic voids emerge between the cured rubber strands on a minuscule scale.

For closed-cell types, manufacturers inject a puff of extra steps. Pressurizing the rubber mass while heating helps shape its morphology. Simultaneously, a nitrogen-releasing additive fills the emerging air pockets. This prevents their collapse while setting for a durable, flexible product.

Cooling completes the formation, yielding sheets and blocks of sponge material. Some receive secondary modifications like addition of other polymers, plasticizers or colorants before shipping.

Comparing Properties of Foam Rubber vs. Sponge Rubber

Both offerings have advantages depending on requirements. Here are some notable properties you should consider:

  • Service Temperature– Foam Rubber performing best as a flexible insulator around -25 to 80 degrees Celsius. Sponge rubber forms firmer coils or sheets, commonly used in automotive and appliance seals from -50 to 150 degrees.
  • Density– The dense yet permeated structure of sponge rubber makes it only one third as heavy as foam rubber. Its looser composition impacts other attributes.
  • Elasticity– Sponge rubber’s interconnected gaps grant it a bouncier, more flexible feel. Foam rubber’s isolated gas bubbles compromise elasticity.
  • Moisture resistance: Closed-cell sponges greatly impede water due to their balloon-like sealed gaps. Foam rubber and open-cell varieties are more efficient at soaking up water.
  • Heat transfer: The poor conduction of sponge rubber’s numerous gaps earns it use as a thermal insulator, outperforming foam rubber in this regard.
Foam Rubber Structure
Foam Rubber Structure


· Uses of Sponge Rubber

Its porous texture, elasticity and moisture resistance makes it suitable for medical, industrial and food industry applications like pads, seals, trims, padding and flotation devices. Open-cell varieties also find use as cleaning tools and drain clogs for their absorbency.

· Uses of Foam Rubber

Foam rubber excels at cushioning due to its compressibility and resilience, appearing in mattresses, furniture, sports safety gear, flotation devices. Automobiles also utilize its energy-absorbing qualities in seats, headliners, engine mounts.


With the above information, you can choose whether foam rubber or sponge rubber is suitable for your applications or not. At LEGENDAY, we offer a wide range of rubber products including foam and sponge. For all your rubber products, contact us now.

More resources:

Silicone Sponge Sheet – Source: LEGENDAY

Silicone Foam – Source: LEGENDAY

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