When Ferrari introduced the 308 GTB in 1975, the company made an unusual decision that would distinguish the earliest examples from almost every other production Ferrari. Instead of constructing the body from conventional steel or aluminium, Ferrari chose fibreglass, creating a lighter sports car that became known as the 308 GTB Vetroresina.
Although the experiment lasted less than two years, it produced one of the most interesting versions of the Ferrari 308. The decision was not simply about reducing weight. Production methods, manufacturing costs and customer expectations all influenced the development of the car.
Photography: Collecting Cars & Ferrari
The 308 GTB arrives
The Ferrari 308 GTB made its debut at the 1975 Paris Motor Show, introducing a new generation of compact sports cars with a V8 engine positioned behind the passenger compartment. Designed by Leonardo Fioravanti at Pininfarina, the model combined elegant proportions with a distinctive rear section featuring flying buttresses, which are the sloping body panels connecting the roof to the rear wings. Its appearance represented a significant departure from the softer shapes of earlier Ferrari models, including the Dino 246 GT.
Although the 308 GTB was a new model, its mechanical foundations were closely related to the Dino 308 GT4, introduced in 1973. Both cars used a 2.9-litre V8 engine mounted transversely behind the seats, meaning the engine was positioned across the width of the vehicle rather than along its length. The 308 GTB was designed as a two-seat berlinetta, offering a more focused driving experience than the four-seat GT4 while establishing the appearance that would influence Ferrari's V8 sports cars for years.
What does Vetroresina mean?
Vetroresina is the Italian word for fibreglass, a material made by combining fine glass fibres with a resin that hardens into a strong structure. Unlike conventional steel body panels, which are pressed or shaped from sheets of metal, fibreglass panels are formed using moulds. This process allows manufacturers to create complex shapes without requiring the same expensive equipment used for large-scale steel body production.
The material was already familiar in motorsport, where reducing weight was particularly important. Manufacturers including Lotus had used fibreglass extensively, while Ferrari's coachbuilding partner Scaglietti had experience working with composite materials on racing cars. However, fibreglass remained unusual for expensive Italian grand tourers, where customers traditionally expected carefully finished metal bodywork. Ferrari's decision to use the material on the 308 GTB therefore represented a significant departure from established manufacturing practices.
Why Ferrari chose fibreglass
One of the main advantages of fibreglass was its relatively low weight, which allowed Ferrari to create a lighter car without making substantial changes to the engine or chassis. The original 308 GTB had a quoted dry weight of approximately 1,090 kilograms, considerably less than the later steel-bodied versions. Lighter vehicles generally need less energy to accelerate and respond more quickly to steering and braking, making weight reduction particularly valuable in a sports car.
Fibreglass also offered practical manufacturing advantages during the early stages of production. Creating body panels using moulds required less investment in large metal pressing equipment, making the material attractive for a manufacturer producing relatively small numbers of vehicles. Ferrari could begin manufacturing the new 308 GTB without immediately committing to the tooling required for higher-volume steel production, while Scaglietti's existing experience helped make the unusual construction method possible.
Fioravanti explains the decision
Leonardo Fioravanti, the designer responsible for the Ferrari 308 GTB, later explained that the car had been developed with fibreglass construction in mind from the beginning. In an interview with Classic & Sports Car, he confirmed that reducing weight was an important advantage and that the original design had been created to accommodate either fibreglass or steel body panels. This flexibility would become important when Ferrari reconsidered the manufacturing process.
Fioravanti also explained that Scaglietti had already gained experience producing fibreglass components for Ferrari racing cars, making the coachbuilder a suitable partner for the project. The decision was therefore not an unexpected experiment introduced late in development, but part of the original engineering approach. However, the design team's ability to accommodate different materials meant Ferrari could change its production strategy without completely redesigning the exterior of the 308 GTB.
The lightweight body’s advantages
The fibreglass body contributed to the 308 GTB's relatively low weight, allowing the car to make effective use of its naturally aspirated V8 engine. Naturally aspirated means that the engine draws in air without assistance from a turbocharger or supercharger. The European-specification engine produced 255 horsepower at 7,700 revolutions per minute, giving the lightweight berlinetta strong performance for a road car introduced in the middle of the 1970s.
Ferrari quoted a maximum speed of 252 kilometres per hour for the 308 GTB, demonstrating that the combination of its V8 engine and lightweight construction was capable of delivering serious performance. However, the fibreglass body was not the only factor influencing the driving experience. European examples also used dry-sump lubrication, a system that stores engine oil in a separate reservoir rather than relying on a deep oil pan beneath the engine. This allowed the engine to be installed relatively low while maintaining reliable lubrication during demanding driving.
Why Ferrari switched back to steel
Despite the advantages of fibreglass, Ferrari eventually decided that steel was better suited to the continued production of the 308 GTB. One of the main problems concerned the quality of the finished body panels, particularly the difficulty of achieving the consistently smooth surfaces expected from an expensive sports car. Fibreglass could develop slight irregularities during manufacturing, making it more difficult to achieve the precise appearance associated with Ferrari's traditional coachwork.
Fioravanti later confirmed that achieving consistent surface quality was an important reason for the change. He also recalled that some Ferrari dealers, particularly in Britain and the United States, were uncomfortable with the idea of selling an expensive sports car constructed from a material associated with less prestigious manufacturers. These concerns help explain why Ferrari returned to steel despite the weight advantage of fibreglass. The change also allowed the company to use more conventional manufacturing methods as production of the 308 increased.
Ferrari began introducing steel bodywork during the later stages of 1976, initially producing both types alongside one another. The transition was gradual rather than a complete redesign introduced at a single motor show. By June 1977, production of the fibreglass version had ended, leaving the steel-bodied 308 GTB as the standard model for the remainder of its production life.
The change increased the car's weight, with differences of approximately 100 to 150 kilograms frequently quoted when comparing early fibreglass examples with later steel versions. However, exact comparisons depend on the specification and measurement method used. The steel body also made the 308 GTB more suitable for larger-scale production, while the exterior design remained almost unchanged. Most customers would have found it difficult to distinguish the two versions without examining specific bodywork details.
Recognising a Vetroresina
One of the easiest ways to identify an original fibreglass 308 GTB is to examine the area where the windscreen pillars meet the roof. Early Vetroresina examples generally have a visible joining line in this area, while steel-bodied cars have a smoother transition between the panels. This small detail provides a useful indication of the construction material without requiring the bodywork to be dismantled.
However, identifying an original Vetroresina requires more than checking a single exterior detail. Specialists also examine the body structure, production records and chassis number to confirm that a car left the factory with fibreglass panels. Because these cars are now valuable collector vehicles, some have undergone extensive restoration or received replacement panels during their lives. Therefore, a proper inspection should establish the originality of the bodywork rather than relying entirely on its current appearance.
How many were built?
The exact production total of the Ferrari 308 GTB Vetroresina remains a subject of disagreement among historians and specialists. Numerous Ferrari reference works quote a figure of 808 examples, while respected Ferrari historian Marcel Massini and other specialists have cited a lower total of approximately 712 cars. The difference reflects the challenges involved in interpreting historical production records and identifying individual chassis.
Regardless of which figure is used, the fibreglass version represents only a relatively small proportion of overall Ferrari 308 production. All original Vetroresina examples were GTB berlinettas, as the 308 GTS with its removable roof was introduced after Ferrari had moved towards steel construction. This distinction is important because it means that an original factory-built fibreglass 308 GTS was never part of the regular production range.
The Vetroresina legacy
Today, the Ferrari 308 GTB Vetroresina is valued for its unusual construction, historical significance and connection to the early development of Ferrari's V8 sports car range. Its lightweight body makes it different from the more familiar steel versions, while its limited production adds another dimension to its appeal among collectors. The model also represents a period when Ferrari was willing to experiment with unconventional materials to improve performance and simplify manufacturing.
The decision to abandon fibreglass demonstrates that engineering advantages do not always determine the success of a manufacturing method. Although the material reduced weight, Ferrari ultimately placed greater importance on production consistency, surface quality and customer expectations. The Vetroresina therefore remains an interesting example of how practical manufacturing considerations can shape the history of a sports car, even when the original engineering concept offers clear performance benefits.
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