During the 50ies and 60ies a lot of cars and car bodies have been created using fiberglass (others may call it plastic, but it isn't really, polyester was another term). Thanks to this material even small production runs could be made profitable and much more variety was possible.
Especially the US had a strong fiberglass era, resulting into brands such as Brooks Boxer, Glasspar, Ascot, Woodill Wildfire, Irwin Lancer, Scorpion, Wasp, Edwards, Grantham Stardust, Venus, Meteor, Kurtis, Maverick Sportster, Victress, BMC Singer, Vale, Allied, Atlas, Multiplex, Bosley, Lasaetta, Chicagoan, Lightning, Rockefeller Yankee, Triplex, Hollywood Plastics, Snohomish Plastics, Almquist, Alken, Sorrell, Bangert, McCormack, La Dawri, Kellison, Byers, BoCar, Devin, LeMans Coupe to name just a few.
For people interested in these cars and components there's a great online resource: Forgotten Fiberglass. Have a look and you'll be amazed of what has been built during these years.
For German speaking people there's a summary and an interesting gallery on this era on zwischengas.com.