An Introduction to Material Selection for Body Kits

A body kit is a collection of exterior modifications to a car, typically composed of front bumper and rear bumpers, side skirts, spoilers, and sometimes front and rear side guards and roof scoops. These body kits are designed to mimic the look of a racing car without the need for the functionality they provide, such as down-force and weight savings.

Body kit parts come in fiberglass, polyurethane, ABS plastic, carbon fiber and composite. There are many companies that offer alternatives to the original factory appearance of the vehicle. Body kits components are designed to complement each other and work together as a complete design. Despite this, the 'mix and match' approach is often seen on cars, where the front of one body kit will be matched with the rear of another.

So, for today we would like to share some information on what materials are used for car body kit and its pros and cons.

1.      Fiberglass (FRP)

Fiberglass is the most common material used for body kit parts. Fiberglass parts are relatively easy to produce and inexpensive to buy, but their fit and finish as delivered is not as good as parts made from polyurethane or ABS plastic. They're lightweight and won't warp regardless of the temperature, and paint readily adheres to fiberglass. The downside to fiberglass is its rigidity. This lack of flexibility makes fiberglass more difficult to install and makes the finished product much more vulnerable. Because fiberglass parts can be rough coming out of the mold, they usually require more finishing than polyurethane parts for an acceptable end product.

Fitment: Totally depends on skills of the crafter.

Pro: Hard, light weight and can easily be repaired when damaged. Able to customize in small quantity. As little as one piece. The cheapest option available.

Con: Brittle, easily crack on impact. Left and right side might not be symmetrical. Again, it depends on the crafter.

Best for: Affordable full body kits, single or small quantity customized parts.

2.      Poly-Urethane (PU)

Polyurethane, also known as just urethane, is another popular material for body kit parts. Urethane (PU) products are made with a closed mold process and the finished product resembles an OEM product on your vehicle; therefore they are more expensive to buy. However, the as-delivered fit and finish is usually superior to fiberglass. As mentioned earlier, polyurethane is much more flexible than fiberglass, making it easier to install and more durable. A polyurethane part can be "coaxed" into position during installation without fear of it cracking, and the end product will flex in response to a minor impact instead of cracking or breaking.

And while the finish on polyurethane parts is generally better than fiberglass, getting paint to adhere to them can be more difficult. They require more specialized preparation to ensure a quality finished paint job, or the paint can flake or peel off. Also, Urethane aerodynamics consists of pliable plastics which make the ground effects more susceptible to heat, causing it to lose its shape, warp, and even tear during usage. Keep in mind that once urethane parts lose shape or rips, it is not repairable leaving consumers no other choice except to spend more money on another product. Urethane aerodynamics are recommended for the high end consumer who does not mind spending more money for a high quality product. Polyurethane parts are heavier than fiberglass, so they're generally not a good choice for a race car, where reducing weight may be a primary goal.

Fitment: Usually, perfect fitment. The body kit is drawn up on computer using CAD software. High precision CNC machines are used to make the mold.

Pro: Long lifespan, light, soft, flexible, does not easily get damage on impact. The thinner the material, the more likely to retain its shape.

Con: Soft can be a weakness too. If used for big items like bumpers, it can deform at high speed. If material is thin, it can get damaged easily. If material is thick, it will be too heavy. Deforms at high temperature. Brittle and breaks easily at very low temperatures. Not able to repair when damaged.

Best for: Lips spoilers, rear spoilers

3.      ABS

 ABS plastic is a thermoplastic made by polymerizing styrene and acrylonitrile in the presence of polybutadiene. The result is a material that combines the strength and rigidity of the acrylonitrile and styrene polymers with the ruggedness of the polybutadiene rubber. ABS plastic is impact, chemical and heat resistant, and widely used by the Original Equipment automobile Manufacturers (OEMs) for body panels. Like polyurethane, ABS plastic is a high quality material with superior fit and finish, which is more expensive and heavier than fiberglass. It's somewhat less flexible than polyurethane but easier to paint.

Fitment: Usually perfect like PU.

Pro: Light weight, cost less PU and PP+PE. Smooth and better surface for paint jobs. Looks better than fiber glass.

Con: Soft, must mix with other plastic material to get into the best condition for body kit. If factory has not enough experience, product might deform or break easily. Harder than PU and PP+PE. Can be easily damaged on impact. Cannot be repaired if damaged.

4.      Carbon Fiber

Carbon Fiber, or more accurately carbon fiber reinforced polymer, is a polymer like epoxy reinforced with carbon fibers. Carbon fibers are constructed from carbon atoms bonded together in crystals that are more or less aligned parallel to the long axis of the fiber. This alignment makes the fiber very strong for its size. The fibers are woven into the fabric that gives carbon fiber its distinctive appearance. Carbon fiber parts are very strong and very light weight, making them ideal for race cars or anyone that needs strength without the weight penalty that comes with metal. However, for most average street cars, carbon fiber parts are installed more for their looks and performance image than any functional improvement. Carbon fiber parts usually come clear coated and ready to install right out of the box. The most significant downside to carbon fiber parts is that they are very expensive compared to other materials. However, a cost effective way to go is to mix parts. For example, choose fiberglass or urethane for the lip spoiler, air dam and side skirts, and then spring for a carbon fiber hood.

Fitment - Like fiberglass, it is usually handmade. Fitment is usually not 100% perfect.

Pro: Very light and very strong. High quality carbon fiber looks very nice.

Con: Very expensive. Cannot be repaired when it is damaged. Does not look nice when there are complicated edges or curves.

Best for: Light weight racing grade parts like GT Wings, hoods and trunk doors.

A final point to consider:

Make sure that the shop you choose to install your parts has experience installing body kits. Just because a shop has years of experience in auto body repair it doesn't mean they're qualified. Installing body kits requires special expertise and it would probably be best to consult with whoever will be doing the work before you make a purchase. Regardless of the body kit material you choose, the end result will only be as good as the quality of the installation.