Polyurethane and ABS: What’s the Difference and What’s Better?

Plastic has long been a go-to material in the automotive world. It’s also been something that’s subjected to verbal abuse on account of both misunderstanding and common myth. We’re not here to talk about how plastics stack up against other materials commonly used on automobiles. But, suffice it to say, that it’s way stronger than most people think. Instead, we are here to talk about two very prevalent types of plastics in the automotive industry— Polyurethane and ABS —and how they compare to one another.

Sure, we all get giddy thinking about the iron and aluminum in our cars. But, truthfully, the plastics and polys of the world are what really put the proper finishing touches on a vehicle. So, in addition to unpacking their similarities and differences, let’s explore what kind of products they’re used to create and whether one is better than the other. To help us further understand the topic, we turned to Billy Longfellow, VP of Design at AirDesign USA. With decades of experience under his belt, he possesses a keen understanding of these materials.

But first, why not metal or fiberglass?

While metal is an ideal material in terms of durability, it’s not always the most practical solution for certain accessories. Issues like corrosion, weight, and cost come into play. Sheet metal can often be difficult to work with for manufacturers, as it needs to be stamped into shape. So, not only is the material more costly than polymers and plastics, but so is the necessary machinery. And when you factor in the issues that the elements pose on these materials (unless properly finished and cared for), they just aren’t the most viable solution.

So, what about fiberglass? Well, in the past, fiberglass was used by many automakers to produce lightweight components like hoods, and is still pretty widely available today. But, while it has its advantages, fiberglass is difficult to manufacture. Additionally, it has to be worked by hand, meaning that the fit and finish can vary and natural defects will show. Plus, while fiberglass has good load-bearing strength, it doesn’t hold up exceptionally well to impact situations, meaning it can crack under shock.

Long story short, there are some areas where plastics and polyurethanes are the only solution. Now, these materials can vary in terms of the manufacturing process, too. But, generally speaking, they are more affordable and easier to work with than metal on a grand scale. Not only that, they don’t rust or corrode like metal, and they’re lighter and more forgiving on other materials.

What exactly is ABS plastic?

But let’s get back to it. What is ABS plastic, anyway? What is polyurethane? And what is the difference?

ABS is an acronym for acrylonitrile butadiene styrene. This is a strong thermoplastic polymer commonly used on the exterior of vehicles in the form of mud flaps, fender flares, trim, and so on. For reference, “thermoplastic” implies that the material gets soft when heated and hard when cooled. In fact, thermoplastic materials can go through these heating and cooling cycles several times without changing their fundamental makeup. That is, unless you heat it to its melting point or freeze it to the point of fracture. However, even then, the material isn’t a waste.

“Thermoplastics are defined as polymers that can be melted and recast almost indefinitely,” explains PlasticsEurope, a leading trade association that represents plastics manufacturers. “These characteristics, which lend the material its name, are reversible, so the material can be reheated, reshaped, and frozen repeatedly. As a result, thermoplastics are mechanically recyclable.”

How is this different from polyurethane?

Polyurethane is similar to ABS in strength and versatility, but ultimately is created and applied differently. Think of polyurethanes more like a combination of rigid plastic and strong rubber. This construction makes them very durable but a little trickier to recycle.

Unlike ABS, which is a thermoplastic, polyurethane is a thermosetting plastic. That means, it forms really strong bonds when heated up—making it great for heat-resistant products. (Think: insulation.) However, that also means it can’t be repeatedly melted down and recast into new parts. That doesn’t mean polyurethane can’t be recycled, just that the process is a little more complex.

“Polyurethanes exist in a variety of forms, including flexible foams, rigid foams, chemical-resistant coatings, specialty adhesives and sealants, and elastomers,” explains the American Chemistry Council. In your car, you can find polyurethane used for interior parts such as the flooring and even bushings in the suspension.

What are the pros and cons?

“They both have their pitfalls,” says Longfellow. “Both are going to grow and shrink with the weather. The problem with ABS is that you don’t have a backside to it. It’s a one-sided mold. So, it’s basically like putting a glove on your hand that’s vacuum-forming. Urethane would be like you’re missing a hand and you can inject that hand. You could have an A and B side of a mold and you could have a back side of it for attachment.”

Generally, polyurethane is a favorite among engineers, not only because it can come in both rigid and flexible forms, but also because it’s a very tough material and can withstand high-stress environments. Furthermore, it is resistant to harsh environmental factors such as heat, oil, and acids.

However, this is not to say that polyurethane doesn’t have its drawbacks, too. “Urethane in its natural state is white, so most people put a carbon black in it to hide all the imperfections,” explains Longfellow. “Plus, urethane is not UV-stable, so it has to have a coating on it. The advantage of ABS plastic is that you can have an extrusion. Extruded plastic can have a DOC coating, so you don’t have to paint it. That’s why you’ll see all of these fender flares in black or satin black—because it already has the coating. Urethane doesn’t have the coating, so over time it’ll turn chalky white,” he adds.

Although ABS plastic may not offer the same level of resiliency, it has high rigidity and impact resistance. And even in low temperature conditions or over long periods of time, ABS plastic will retain these characteristics. And, like Longfellow points out, a benefit in ABS’s corner is the finish. This material is very appealing to the eye even in raw form and it’s easier to paint than polyurethane.

This isn’t to say that polyurethane can’t be pretty, too. (In fact, some exterior parts, such as spoilers, are constructed of it as well.) But, overall, its characteristics lend it more toward performance than styling. Longfellow sheds a little light on why this is: “The urethane is going to grow longer. Let’s say you have a side skirt on a F-150. That thing is going to grow maybe a quarter of an inch by the end of the summer. So, what’s going to happen is it’s going to have a bow in the middle because it’s going to buckle out.”

But because of its versatility and toughness, polyurethane is often found in areas where abuse is the name of the game. Typically, we find this material used for seat foam, in the windows, flooring, and even in the bumpers. Furthermore, the fact that polyurethane has strong sound absorption means it’s often used for suspension bushings, which is something many drivers are seriously thankful for.

What are the real-world advantages of one over the other?

So, on paper it might seem like polyurethane is the chief winner, right? Well, sure, but we should take a look at it from the manufacturer’s perspective. Polyurethane is complicated to produce. And, let’s not forget, recycling can be a hassle, too—a drawback that can be very costly as the world turns toward greener initiatives. In short, “complicated” means “expensive,” which means higher production costs and higher consumer costs.

So, yes, polyurethane is stronger than ABS plastic. And, yes, it can stand up better to high-heat environments. But in a real-world consumer scenario—say, when purchasing fender flares—how much does this really matter? You’re not off-roading on Mars. Those ABS parts on your Jeep can easily withstand the typical impact, heat, and chemical abuse found on the trail and look better doing it—all at a lower price to boot.

However, as mentioned, when seeking parts that are going to see major, prolonged abuse—you want a material that can stand up to the challenge. And, in that case, polyurethane will gain your vote of confidence.

So…why not use both?

Let’s not ignore the 800-pound gorilla named “Technology” in the room. We live in the future! Innovation has given us the means to overcome incredible leaps and bounds! In the latter part of a decade, we’ve seen electric cars become normalized, smartphones become mega processors, and machinery become (nearly) self-aware.

So, have we begun to harness this information in a way that we auto enthusiasts can really begin to have fun with? The answer is yes.

As stated, ABS plastic and polyurethane have their own advantages in terms of manufacturing. ABS is vacuum-formed and comes with an existing UV-resistance. However, because you only get one-sided molds, there are hurdles to overcome for mounting solutions that are otherwise easily solved with urethane. But on the flip side, urethane isn’t as pretty or UV-friendly as ABS, so you can’t simply develop a product that’s ready to go on the vehicle in its natural form like as you can with ABS.

“The last two years, we’ve been working on this material that we introduced in our SEMA booth,” says Longfellow, referring to AirDesign USA’s impressive new product lineup for the JL Wrangler at SEMA 2019. “We did flares with it, a new grille with it, and we did our new bumper. It’s the combination of both—you can inject it and you could basically hit it with a baseball bat.”

“With this new material, we’re going to be able to start injecting things like fenders and hoods, and that’s something we’re really excited about,” says Longfellow. “Now, instead of making a hood scoop, we’re going to be able to inject a hood—and it’s going to be lightweight and strong, too.”

This new material AirDesign has been working on is specifically designed to marry the best of both worlds—something that could reshape the entire industry! Keep an eye on AirDesign to see what else they do with this technology and be on the look out at upcoming trade shows to see how other aftermarket suppliers are innovating in the sphere.