The look of a wide-body Evo, NSX or 240 has a "shock-and-awe" effect on the soul as it sizzles the retinas. But beyond the fat fenders and low-slung spoilers lies a science teacher's nightmare. The building blocks of today's body kits are full of chemistry-laden formulas. But it boils down to three basic materials:
Fiber-Reinforced Polymer (FRP)
FRP is a composite that is a combination of a polymer matrix and a reinforcing material like fiberglass strands. The type of polymer used can determine the flexibility of the end product. Popular polymer resins include polyester, isopolyester and vinylester.
Polyurethane
In the realm of body kits, polyurethane is produced from ethyl carbamate, a chain of organic compounds and fillers to form a rigid elastomer. Polyurethane and urethane are vastly different materials so don't confuse them. Polyurethane is injection molded into its final form and is characterized by its highly flexible personality. This can be a challenge to paint, requiring special flex agents in the paint. Repairs are also very tricky but the piece can absorb low-shock impacts and retain its shape.
Carbon-Fiber
There are different types of carbon-fiber. The most commonly used in body tuning components is carbon-fiber reinforced polymer (CFRP), also known as wet carbon, which is made in the same manner as FRP but instead of using fiberglass strands as the reinforcement entity, carbon-fiber strands are weaved into a fabric that serves as reinforcement. The weaved carbon-fiber material gives carbon-fiber parts their checkered look and added strength. In most cases, CFRP materials have a laminate structure, providing reinforcing in two perpendicular directions. The polymer combined to the carbon-fiber weave is usually epoxy but polyester, vinylester and nylon can also be used.
On a near-molecular level carbon-fiber consists of extremely thin strong fibers (.005mm to .010 mm). It's an engineer's dream come true - a material that's lighter than aluminum but also pound-for-pound stronger than steel. This makes it ideal for the construction of things like surfboards, 65% of Lexus' new LF-A and even aircraft like the Boeing 787 Dreamliner. In reality, carbon-fiber is a bit over-engineered for the limited stress seen in body kits.
The big advantages of carbon-fiber include its lightweight, high strength-to-weight ratio, high fatigue strength and how it can be formed into almost any shape. On the minus side of the ledger we find its high cost.
Some of the other buzz words to decipher before deciding on a body kit have to do with how the parts in question are formed:
Compression Mold
To make an item like a fender, the carbon-fiber weave cloth can be draped or layered into a mold of the fender. Called the compression mold process, the back-side of the mold is secured in place then epoxy is poured into the mold. The piece is cured by heat or ambient air. This is a quick process that is used for high-volume parts but it can be difficult to control the amount of resin used. This method can sometimes lead to horribly fitting parts.
Vacuum Mold
Used for low-volume parts, vacuum-molded pieces can be manufactured by wet lay-up that introduces the two-part resin already mixed or via induction that has the fabric weave placed in the mold and the resin pulled into the piece via suction. The vacuum process allows for a near-perfect image of the mold.