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aerohead -

Originally Posted by aerohead

Porsche Engineering rejected the space frame in the mid-1990s citing, that after evaluation , lower upper body strength,especially along the roof rail would not handle the crash energy of a Body-In -White hybrid steel unibody developed to the UltraLight steel auto body ( ULSAB ) specifications.
I believe GM used sheet molding compound SMC for Saturn cars body panels along with Reaction Injection Molding (RIM) for the fascias.
Safety may have pushed GM away from plastics,as crash energy absorption during destructive deformation of the steel unibody probably has the edge.
It has been claimed that carbon fiber will never go down in price.
Carbon fiber ( polyacrylonitrile ) is made from pitch or Orlon heated in a vacuum until oxidized.It's all hydrocarbon.

Found this by accident today :

GM unveils Saturn: skin is half thermoplastic. | Automotive > Automotive Overview from AllBusiness.com

All vertical body panels and bumper fascia on the Saturn models are injection molded thermoplastics. The panels are bolted to the steel space-frame understructure, complementing the steel horizontal body panels, and making Saturn the first true high-volume vehicle platform making extensive use of TP body panels.

While there will be three different Saturn models introduced this year (a two-door sports coupe and the SL1 and SL2 four-door sedans), manufacturing engineers indicate that the facility has capability for producing two additional body styles in coming years.

Materials used for the major body panels include Noryl GTX 910 PPO/nylon alloy form GE Plastic for fenders and quarter panels; Pulse B250 PC/ABS from Dow Chemical for door panels, rocker panels and lower deck-lid panels; HiFax ETA-3095 TPO from Himont Inc. for upper and lower front bumper fascia; and an unnamed proprietary HiFax TPO grade for rear bumper fascia. On the two-door sports coupe and SL2 four-door model, the doors are split into interlocking upper and lower panels, providing two-tone paint flexibility for variations in body styling.
...
DIMENSIONAL ACCURACY VITAL

In previous thermoplastic body-panel applications, dimensional stability was a key concern, and often a crucial stumbling block (see PT, Sept. '89, p. 84). Saturn engineers say they anticipated some problems with maintaining dimensional stability of thermoplastic panels and therefore designed wider margins between each panel. While these fit margins are slightly wider than on most compact cars, the engineers say it was "a worthwhile tradeoff," given the advantages derived from the polymer panels.

CarloSW2