Since the late '50s the automotive reproduction market has embraced glass fiber for its many advantages, including low cost and simple manufacturing. One of the benefits of glass fiber is the potential for a self-supporting structure that doesn't require reinforcement using other materials.

Boats are an example; having minimal open or 'cut out' areas proportional to the total area of the structure for good reason. Open areas reduce stiffness due to the fact that loads can't be carried across them.

Racing cars almost universally feature some sort of protective roll cage and therefore can use relatively thin, lightweight composite panels. This type of body doesn't require the same functionality that a street car does, and usually don't have opening doors or a boot. Top Fuel funny cars are a perfect example of this, where the use of glass fiber results in a lightweight, non-structural body with very few open areas.

Contrasting this, automotive bodies designed for street use feature a high proportion of open areas such as doors, boot, and the cockpit opening on convertibles. As a result, achieving adequate stiffness requires a lot of glass fiber and there's a weight penalty in this.

In motor sport, glass fiber can offer substantial weight saving benefits, however this doesn't usually translate to street car...

It's something of a vicious circle, as the more material required to make a glass fiber panel stiff, the heavier it gets; and the heavier it gets the more material is needed to support the structure. Some reproduction manufacturers promote their use of Coremat® to produce a 'core' or sandwich structure that increases panel stiffness. However, while this material increases stiffness it's also porous - meaning it absorbs resin - and this contributes to increased weight.

Relying on glass fiber for protection in an automobile accident has its limitations. Many reproductions use wood reinforcing, while most good quality reproductions use only lightweight steel for body support and localized reinforcement where door hinges and locks mount - this providing little if any passenger protection in an more

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