Solids based on organic polymers which can either be produced synthetic or which are modified natural substances. The two basic groups of polymeric solids are thermoplasts and duromers. Thermoplastic substances can sustain multiple melting-freezing-processes and moulded products are produced by injecting the melt into moulds. Duromere substances once beeing transformed into a solid state can never again become fluid without destroying the polymeric nature.
Plastics, if not modified by additives, are very good thermal and electric insulators. Their density, if not expanded, is within the limits of 0,9 g/cm² and 1,5 g/cm². In general they are inflammable. Their hardness, stiffness and strength usually is below metallic materials. Some duromers have elastomeric properties (rubber, elastic elongation (much) more than 100%) and some copolymers of thermoplasts as well (thermoplastic elastomeres TPE).
Properties of plastics can be dramatically modified by additives, so that they, for example, can be electrically conductive or may become higher stiffness than steal by forming composites with high performance fibre reinforcement.
A common feature of all plastics is their low surface energy which is responsible for generally difficult bonding, coating or painting. The surface energy can be increased by plasma activation or plasma etching so that perfect bonding of almost any material is enabled.