What are some lightweight materials that are NOT PLASITIC-(oil) but hold up similair to plastic?

Question

IF you look at the link bellow they are interested in light weight materials that are not plastic which uses oil but holds up like plastic. Materials like wood wouldn't work well. Anyway does anybody know if their are any?

http://www.allconferences.com/conferences/20040408153009/

Answer 1

Ford (automobiles) has been advertising a soy-based foam plastic that they are using for seat cushions and mouldings.

Other than that...???

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