What are these seat out of?

From Paul Harvey. Now heres the rest of the story. 1968 and 1969 A & B body bucket seat cars all used the same seat frames, with different upholstery between divisions and models. Head restraints were optional up to january 1969. After jan 1st 1969 per DOT regs, head restraints were mandatory on all new passenger car front seats, bucket seats included. Nice dart by the way.