[EXTERIOR] Body Kits, Fiberglass vs Polyurethane vs Carbon Fiber
Body Kits, Fiberglass vs Polyurethane vs Carbon Fiber

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Fiberglass has been used in the automotive aftermarket scene for many years, and it continues to be used on bodywork despite the gaining popularity of carbon fiber.

The advantages of fiberglass are:
- Its usually the least expensive alternative.
- Fiberglass has been around for a long time in a variety of automotive and non-automotive uses. Many people can install and repair it.

The negative aspects of fiberglass are:
- Fragility in some uses, including its possibility to chip, spider, and shatter.
- Weight penalty when compared to carbon fiber.

Before manufacturers began to readily experiment with products other than sheet-metal, the Chevrolet Corvette was known as a "fiberglass sports car," for the sheer novelty of its pioneering use if nothing else.

Lightweight and relatively easy to produce, fiberglass offered some benefits over heavier and more corrosion-prone metals, but had its downside, mainly unpredictable and thorough failure in collisions.

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Carbon fiber
Carbon fiber, the material first used by NASA on spacecraft, has become ubiquitous in the tuner scene. Of course, as with most performance add-ons, its popularity has as much to do with its appearance as its performance. From a structural standpoint, carbon fiber has a very high tensile strength to weight ratio, making it an ideal alternative in applications like body panels and aero components where lightweight fiberglass and aluminum might have otherwise been used. Carbon fiber has a naturally shimmering look to its alternating gray and black checkered weave, and many auto enthusiasts prefer to mount it as-is rather than painting over this attractive surface.

However, carbon fiber has its negative aspects:
- Although light and strong, carbon fiber is anything but cheap. The raw material (available in rolls or pre-impregnated sheets) is expensive.
- For the weave to look cosmetically acceptable, the lay-up process must be flawless and uniform. Because carbon fiber is often kept bare and on display, cosmetic perfection is an important consideration in the manufacturing process.
- Hit at the wrong angle, carbon fiber splinters and shatters where metal would bend and crumple.
- Carbon fiber is both Flammable and Electrically conductive.
- Carbon fibers appearance degrades with exposure to ultraviolet rays, becoming brown and hazy.
- When used to make hoods, carbon fiber requires the use of Hood pins to prevent it from unlatching and smashing the cars windshield. There have been numerous instances of ultra-lightweight carbon fiber hoods flying up and smashing the windshield and windshield support pillars (and yet sustaining no damage to the Hood itself).

A typical carbon fiber Hood sells for $500 to $900 and, depending on model and application, components run between $200 for a budget-level spoiler to well over $1000 for top-shelf limited-run items. When shopping for carbon fiber, keep in mind that not all carbon fiber components are created equal.

Carbon fiber costs vary depending on:
- Grade of weave
- Fitment
- Lay-up method:
  * Wet lay-up involves laying up sheets of carbon fiber cloth in resin, much like traditional fiberglass work. The resin is applied with a squeegee in the mold, and gravity sets the carbon fiber in shape as it cures. This is the cheapest and simplest method of making carbon fiber. These products arent as light and strong as dry lay-up.
  * Dry lay-up uses pre-impregnated (pre-preg) sheets of carbon fiber that are either set by vacuum bagging or baked in an autoclave to achieve a stronger and lighter finished product. Dry lay-up carbon fiber can often be distinguished from wet lay-up by the lack of the high sheen from the resin, and the fact that the
weave of the fabric can often be felt (in wet-lay up, the additional resin creates a perfectly smooth surface).
- Pressure setting:
  * An autoclave is a pressure oven that cures carbon fiber at a specified temperature while using pressure to adhere it to the mold.
  * Vacuum bagging sets the mold inside a bag in which a pump creates a vacuum, setting the mold under pressure.

A variant on carbon fiber, carbon/Kevlar is the stronger alternative to pure carbon fiber, but is generally heavier as well. Carbon/Kevlar weaves can often be identified by the yellowish weave (the color of the Kevlar strands) against the gray/black of the carbon.

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For a long time, polyurethane has been a staple of car manufacturers for its ability to give and to recover from minor impacts, polyurethane is gaining popularity in the tuner world as the material of choice for:
- Bumper covers
- Side skirts
- Lower lips

Any part of the car exposed to impact or road debris can be made much more resilient and long lasting with polyurethane than with fiberglass or carbon fiber.

Polyurethane has a few drawbacks:
- Weight (compared to carbon fiber)
- Cost
- Lack of stiffness

Polyurethane is an inherently flexible/non-rigid material, so it isnt ideal for body components that have large surface areas, such as hoods and trunks.

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Further reading: Body Kits, Fiberglass vs Polyurethane - Myths & Facts...