n Originally, a member of a group of synthetic substances which resemble and share some of the properties of natural resins, but now used for materials which bear little resemblance to natural resins. The term is generally understood to mean a member of the heterogeneous group of compounds produced from simpler compounds by condensation and/or polymerization. Chemically modified natural polymers, such as cellulose acetate and hardened casein, are not considered to be synthetic resins. (Flick EW (1991) Industrial synthetic resins handbook. Williams Andrews Publishing/Noyes, New York).