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

Image source:

Doug Sharpe
President of Elasto Proxy

Did you know that there’s a difference between foam rubber and sponge rubber? Sure, the two terms are often used interchangeably. Unless you work in the rubber and plastics industry, the sponge next to your kitchen sink may seem similar enough to the foam mattress pad on your bed. Both substances are soft and squishy, right? Upon closer examination, however, saying that foams are identical to sponges is like saying that doing the dishes is the same as getting a good night’s sleep.

For technical buyers, choosing the right material is a lot more important than finding the right analogy. The memory foam from a mattress might help with after-dinner cleanups, but a polymer kitchen sponge is a better choice. For safety-related applications, selecting the right rubber material may also mean meeting requirements for flame, smoke, and toxicity (FST). In the mass transit industry, for example, some silicone foams meet FST standards but many carbon black foams do not.

What’s so different about these foams, and how does foam rubber compare to sponge rubber anyway? Let’s take a look at how these polymers are made, and consider how raw materials, chemical reactions, and production processes can affect the characteristics of foam and sponge rubber.

How Foam Rubber Is Made

The differences between foam and sponge rubber begin with ingredients and end with molecular structure. Foam rubbers use a blowing agent, typically a gas or a chemical that produces a gas, to create a mass of small bubbles in a liquid mixture. Typically, this mixture contains polyols, polyisocyanates, water, and chemicals or additives such as flame retardants, fillers, and colorants. There are many different types of blowing agents, and foaming is used for both rubber molding and rubber extrusion.

The polyols and polyisocyanates in foam rubber are liquid polymers that, when combined with water, produce a heat-generating or exothermic reaction. By using specific types and combinations of liquid polymers, a material compounder can create flexible or rigid foam rubbers. During polymerization, molecules from the polyols and polyisocyanates crosslink to form three-dimensional structures. The compounder can control foaming by adjusting the amount of water, or by using surfactants.

The importance of blowing agents in the production of foam rubber cannot be overstated. Although you can do the dishes without a sponge and get a good night’s rest without a mattress pad, a compounder cannot create foam rubber without a blowing agent. Typically, flexible foams use the carbon dioxide gas formed by the reaction of water with the polyisocynate. Most rigid foams use hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs), gases with higher levels of toxicity and flammability than found in chlorofluorocarbons (CFCs).

How Sponge Rubber Is Made

Sponge rubber may be similar to foam rubber, but the two are not one and the same. For starters, there are two main types of sponge rubber: open-cell and closed-cell. Open-cell sponge rubber contains open, interconnected pockets that permit the passage of air, water, and other chemicals when the material is not compressed. Closed-cell sponge rubber contains balloon-like cells that hold nitrogen gas and thus prevent the passage of these substances at low pressures.

To produce open-cell sponge rubber, sodium bicarbonate is added to other ingredients in a heated mold. As the uncured sponge rises like a cake, the baking soda creates open, interconnected cells. To make closed-cell sponge rubber, a chemical powder that decomposes under heat and pressure is added. The nitrogen gas that’s released helps to give closed-cell sponge rubber its strong compression set and recovery characteristics.

Although nitrogen is a gas, it doesn’t produce a foam like the gaseous blowing agents used with foam rubber. Foaming is specific production process, and foam rubber contains mostly open cells. Although some of the cells in foam rubber are closed, these rubber materials would not pass ASTM tests for water absorption, a standard requirement for closed-cell materials.

Join the Conversation

Do you need to source foam rubber or sponge rubber profiles? How can we help you? For over 20 years, Elasto Proxy has been solving challenges and providing solutions. Join the conversation today. Look for a post with a link to this blog entry on LinkedIn, Facebook, Google+, and Twitter.

Elasto Proxy has pages on all of these social media websites, so all that’s missing is you. I hope you’ll subscribe to our free e-newsletters, too. They’re a great source of information delivered right to your email inbox, and provide links to blog entries like this one.

Inflatable Bike Helmets and Airbag Technology

Bike Helmet

Image source:

Doug Sharpe
President of Elasto Proxy

This is a picture of a woman wearing a bicycle helmet. The collar around her neck may look like a scarf, but it’s actually an airbag. If she falls from her bike, an inflatable helmet will deploy and provide shock absorption. The pressure will remain constant for several seconds, enabling her to withstand multiple head impacts during a cycling accident. After that, the Hövding begins to slowly deflate.

Safety Meets Comfort

Made in Sweeden, the Hövding airbag helmet is a lightweight but tech-heavy alternative to those traditional plastic-and-Styrofoam helmets that many bicyclists accept but dislike. Available on the Web and in some European stores, this innovative protective device is also a YouTube sensation. So how reliable is the Hövding? Are cyclists sacrificing safety for comfort?

The answers to these questions can be found in the sensors and algorithm that enable the Hövding to distinguish safe biking from cycling accidents. Designed by mathematicians, electrical engineers, and airbag experts, the electronics-equipped collar causes the airbag to deploy during a crash – but not if raindrops or leaves fall atop the cyclist’s head.

When inflated, the Hövding’s airbag provides a larger area of head protection than traditional bike helmets. There’s also a “black box” that captures 10-seconds worth of accident data for subsequent analysis and algorithmic improvements. The company would like bicyclists involved in accidents to share their data, but does not actively monitor Hövding usage.

Electronic Components and Rubber Materials

Bicyclists who wear the battery-powered Hövding can recharge the device via USB connections on computers or mobile phone chargers. The battery lasts for about 18 hours, and uses LED lights and an audible alert to signal that power is low. For cyclists who demand not only comfort and safety but also fashion, there’s a selection of colorful shells for the collar.

During an accident, however, even the most fashion-conscious bicyclist will be grateful for the Hövding’s plain-looking but reliable airbag hood. Made of strong nylon fabric, it won’t rip when scraped against the ground. Like traditional bike helmets, however, the Hövding doesn’t offer whole-head protection. To preserve the bicyclist’s field of vision, the face remains exposed.

The hood’s super-strong nylon is important, but so is the gas inflator that fills it with compressed helium. Housed in a holder inside the collar, this gas-filled canister rests on the cyclist’s back for proper weight distribution. Specifications for the canister aren’t listed on-line, but its control valve probably uses an NBR seal that can withstand helium and aging while maintaining proper pressure.

Rubber Seals and the Evolution of the Airbag

Years ago, I toured an airbag factory. As the co-founder and co-owner of a company that provides custom sealing solutions, I remember thinking how even the mixing machines that make airbag collars require inflatable seals. I also remember learning how airbag technology is tailored to an automaker’s specific needs, and how airbags must account for speed and force.

Automotive airbag technology has evolved significantly since airbags first became required safety features. Airbag injuries, especially to children, have sparked both technical advances and regulatory changes. Today, both passenger cars and light-duty trucks are equipped with sensors that cause front airbags to deploy with less force – or not all. Airbag shapes and sizes are different, too.

Hövding’s technology is impressive, but how well will its airbags last over time? Given a choice between using compressed gas or gas-producing chemicals, North American automakers opted for the latter. In addition to space considerations, engineers worried that a compressed gas canister might not remain at pressure for the life of the car. This concern shows why seal selection is so important, and how a rubber seal must meet all of an application’s requirements.

Join the Conversation

Would you wear a Hövding inflatable air helmet on your next bike ride? Do you need sealing solutions that meet demanding requirements for aging and pressure, and that must resist a compressed gas such as helium?

Join the conversation. Look for my post with a link to this blog entry on LinkedIn, Facebook, Google+, and Twitter. Elasto Proxy has pages on all of these social media websites, so all that’s missing is you!  We also hope you’ll subscribe to our free e-newsletters, a great source of information delivered right to your email inbox.


Rubber Bladders and Rail Shipments of Crude Oil

Oil Transport

Image source:

Clyde Sharpe
President for International Sales of Elasto Proxy

What is the role of rubber in transporting crude oil across North America? Last week, we examined how elastomeric seals support pipeline safety. From risers to wellheads to pumps and valves, the oil and gas industry needs reliable rubber products that meet application requirements for temperature, pressure, and oilfield media. As the U.S.-based Plantation Pipe Line company learned in 2006, gasket failure can release fuel into waterways and result in steep fines and environmental damage.

Closer to home and more recently, Canadians are still coping with the disaster at Lac-Mégantic, Québec, the site of a massive train derailment that burned or spilled 5,630,000 liters of light crude oil last July. Owned and operated by the Montreal, Maine, and Atlantic (MMA) Railway, the freight train included 72 tanker cars traveling from North Dakota to New Brunswick. As rail shipments of crude continue to rise, is there anything that can be done to make oil tankers safer?

Rail Safety and Professional Networking

The summer before the Lac-Mégantic disaster, members of the Frac Sand group on LinkedIn may have discovered a solution. In a discussion about open railcars, the head of a transportation company asked for advice about transporting frac sand, a crush-resistant sand that’s used in hydraulic fracturing. As the conversation considered various technologies, a railway executive suggested using rubber bladders and referred to an article about them in World Coal magazine.

As John Licht, the Director of Business Development at Badger Farm Rail explained, rubber bladders are manufactured to military specifications and designed to withstand high temperatures while transporting diesel fuel. Frac sand has different chemical properties than diesel, of course, but could fuel bladders used in military operations withstand railroad conditions? And could rubber bladders serve as secondary containment systems within steel rail cars that carry crude oil?

Crashworthy and Self-Sealing Bladders

The defense industry may hold yet another lesson for railways that haul flammable fuels.  As the military contractor Musthane explains, crashworthy and self-sealing bladders are used on-board ships, aircraft, helicopters, and armored vehicles. Made of specialty fabrics coated with urethane or nitrile, these fuel bladders often include aramids along with a special foam that helps to balance the liquid in the tank and avoid explosions.

Aerotec Laboratories (ATL) also manufactures crashworthy fuel tanks for military and civilian customers, including NASCAR and Formula One. Recently, the New Jersey-based company also entered the market for unmanned aerial vehicles (UAVs), supplying lightweight fuel bladders made of rubberized fabrics. To produce leak-tight joints, the seams are vulcanized. Fuel bladder configurations include rectangular and cylindrical, as well as radiused edge and convoluted fuselage.

What’s the Answer? 

For Canada’s energy future, the stakes are high – especially in the tragic aftermath of the Lac-Mégantic disaster. Although some may claim that railroads can never be made safe enough, shipments of crude oil are rising – 28,000% in the last 5 years. Could crashworthy rubber bladders in railcars help to avert spills and explosions in the event of another train derailment? What are some other solutions to increase rail safety and avoid another tragedy?

As a supplier of high-quality, custom-fabricated sealing solutions to a variety of industries, Elasto Proxy welcomes this debate and encourages you participate. I hope you’ll comment on this blog entry and share your own knowledge, whether it’s about railcars, petroleum products, or rubber. As the members of the Frac Sand group on LinkedIn can attest, it’s better to work together.

Outsourcing and Custom Fabrication – Industrial Rubber Products


Alex Bergeron
Sealing Solutions Provider at Elasto Proxy

What do you think of when you hear the word “outsourcing”? Do you think of increased efficiency and higher quality, or do you worry about a loss of control? Outsourcing your manufacturing processes to a partner requires trust. That’s why long-term business relationships are important, and why proof can strengthen a commitment.

As a solutions provider for Elasto Proxy, it’s my job to listen to all of your application requirements and business needs before recommending the right sealing solution. Words aren’t always enough, however, and sometimes seeing is believing. Such was the case with a manufacturer of ventilation units who chose custom-fabricated gaskets instead of unfinished rubber coils.

Door Gaskets for Ventilation Units

Ventilation units have access doors that allow maintenance and repair personnel to reach machinery. The gaskets for these doors vary in size, but all require rubber compounds that can meet demanding environmental conditions. With our partner’s vacuum units, for example, exposure to dust, water, and pollution made dual durometer EPDM the right choice.

Manufacturing the rubber gaskets for these access doors can be a labor-intensive process, and produce material waste and unwanted variations. At our partner’s production facility, employees would position the rubber coils that we supplied next to a machine. Production personnel would then unroll the rubber onto the access doors, cutting and then splicing the lengths where they met.

Gaining Quality by Giving Up Control

Performing these operations in-house gave our partner maximum production control, but also created opportunities for increased efficiency and higher quality. Human error and variations between workers or even shifts can cause small differences in cuts and splices. If the rubber that’s left on a coil isn’t long enough for finished product, the remaining material becomes unusable for gasketing.

Although our partner originally wanted a distributor, touring our Boisbriand, Quebec production facility provided proof of Elasto Proxy’s custom fabrication capabilities. Today, our skilled production team cuts their doors gaskets to length and then performs film splicing operations. Improvements to quality and efficiency have strengthened our partner’s supply chain, and strengthened our business relationship.

Asking, Answering, and the Art of Sealing


Doug Sharpe
President of Elasto Proxy

How well do you listen? Do you like to ask questions? When you have the information that you need, do you know what to do with it? Many people think that selling is all about talking. Yes, the ability to speak effectively is important. Salespeople need to write clearly, too, especially when it’s time to communicate instructions. But don’t underestimate the importance of asking for and analyzing answers.

Answers and Application Knowledge

Recently, a group of Elasto Proxy employees visited a Montreal-area restaurant with Andrew Yang, our sales representative in China. Before heading inside, I noticed a front-end loader. Although the operator of this mobile specialty vehicle was busy, he took the time to answer my questions about the door seals. We also talked about the noise, vibration, and overall comfort level inside his cab.

As a custom fabricator of industrial rubber products, Elasto Proxy provides sealing solutions to makers of on-road and off-road equipment. Every application is different, of course, so it’s important to listen to all of the requirements before offering recommendations. In the case of our front-end loader, asking a few questions allowed me to offer some advice about adjusting the floor mats.

Solutions Providers Instead of Salespeople

Several years ago, Elasto Proxy replaced its salespeople with solutions providers. In our Internet Age, there’s plenty of information on the Web – and few people like to be “sold to”. So what do managers, technical buyers, and product designers look for in a potential supplier? In short, they want a partner instead of a provider. By offering solutions instead of products, partners demonstrate commitment.

When I spoke with the operator of the front-end loader, I knew I wouldn’t sell him door seals or anti-vibration components on-the-spot. That wasn’t the point of our conversation. By learning about his user experience, however, I confirmed that the door seals on this particular type of vehicle leak. I also learned that mold under the rubber floor matting is problematic.

The Right Way to Start the Sales Process

In the future, I’ll use what I learned about this front-end loader in my conversations with other mobile specialty vehicle manufacturers. At the same time, I’ll also consider what I don’t know. For example, although I’ve specialized in rubber seals for many years, I don’t consider myself an expert in bearings. But when the operator and I spoke about vibrations and transmissions, I readily shared what I knew.

Asking questions and getting answers is part of the sales process. Applying what you’ve learned to the solutions you can provide is important, too. Just explaining your company’s capabilities is not enough, however. By taking the time to listen and learn, you’ll become a solutions provider instead of a product salesperson. For Elasto Proxy, the art of sealing begins with a question: How can we help you?

Rubber Bumpers for Shock Absorption and Traction

Rubber Bumpers
Rubber Bumpers

Rubber bumpers are solid rubber profiles that provide shock absorption and traction for industrial and commercial applications. They are made of various rubber materials and/or compounds, and can be recessed or threaded per application requirements. Rubber bumpers are available in different shapes and can resist moisture, dust and corrosion. Extruded rubber bumpers are also available.

Rubber Bumpers

When selecting rubber bumpers, product specifications to consider include parameters such as rubber material selection, shape, dust resistance, chemical resistance, and other material and chemical properties. Vendor selection and compliance with industry, quality and/or regulatory standards is also important.