The difference between foam rubber vs. sponge rubber is about how these gasket materials are made and the type of sealing barrier they provide. You don’t have to be a scientist to understand these differences, but you do need to make the right choice if you’re an engineer or a technical buyer.
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Otherwise, you risk choosing a gasket material that could fail in the field when you need it the most.
What does gasket failure look like? If you make the wrong choice between foam rubber vs. sponge rubber (or choose the wrong compound or durometer), your seal could leak or over-compress. The rubber might also shrivel up or become brittle.
At Elasto Proxy, we recommend basing material selection on MTAP, an easy way to remember Material (M), Temperature (T), Application (A), and Pressure (P). Contact us for custom gaskets that provide sealing success or keep reading to learn about the differences between foam rubber and sponge rubber.
Let’s start by taking a look at how foam rubber is made and how it’s used.
Foam rubber is made with what’s known as a blowing agent. Typically, this is a gas or a chemical that produces a gas. The result is a small mass of bubbles (foam) in a mixture of the following ingredients.
What are polyols and polyisocyanates? They’re liquid polymers that generate heat when they’re combined with water. By controlling the amount of foaming and adjusting the volume of water, it’s possible to adjust the foam rubber’s end-use properties.
The type of blowing agent is critical, but the type and amounts of liquid polymers are also important because they can produce either flexible or rigid foam rubber.
How is foam rubber used?
The way that foam rubber is used depends on whether the material is flexible or rigid. Yet it also depends on the specific type of elastomeric compound. Consider these two examples.
These are just a few applications for foam rubber, and there are many other types of products for specific applications. For example, did you know that Elasto Proxy has fabricated foam rubber into elastomeric pads for the vacuum tooling used in stone countertop manufacturing?
Now that you know the basics of foam rubber, let’s take a look at how sponge rubber is made and used. But first let’s look at the difference between open-cell and closed-cell materials.
There are two types of sponge rubber: open-cell and closed-cell.
In other words, the type of cells (open or closed) either permit or prevent the passage of liquids or gases. But isn’t the nitrogen that’s used in closed-cell sponge rubber a type of gas? And aren’t gases used in foam rubber? It’s time to take a deeper dive.
Yes, nitrogen is a gas; however, it doesn’t produce foam. Moreover, the foaming process that’s used with foam rubber creates mostly open cells. The closed cells that are produced are too few in number for foam rubber to resist water absorption.
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So how is open-cell and closed-cell sponge rubber actually made?
To produce open-cell sponge rubber, sodium bicarbonate is added to other ingredients in a heated mold. As the uncured sponge rubber rises like a cake, the baking soda creates open, interconnected cells.
To produce closed-cell sponge rubber, a chemical powder that decomposes under heat and pressure is added to a mixture of ingredients. The nitrogen gas that’s released helps to give closed-cell sponge rubber its strong compression set and recovery characteristics.
Sponge rubber profiles are fabricated into finished gaskets for a variety of applications. For example:
These are just a few of the many applications for sponge rubber, which also comes in compounds (such as EPDM and silicone) that provide varying degrees of environmental resistance. The rubber’s hardness (durometer) and the profile’s shape are also important to consider.
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.
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.
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 us to discuss your requirements of rubber foam insulation. Our experienced sales team can help you identify the options that best suit your needs.