Plasticity is the tendency of a material to remain deformed after a deforming stress is reduced to a value less than or equal toits yield point.
Thermoplastic polymers nearly all have high plasticity.
When a given stress is applied to a non-reinforced thermoplastic test piece there is an initial elongation (changing reversibly with the stress in almost linear fashion, provided the load level is not too high), then an elongation that is a function of time resulting from creep of the material. This elongation is quasi-linear with time and non-reversible.
According to how samples are taken and the nature of the resin, composite materials have very low plasticity. It would be more appropriate to refer to the change in degree of damage or initial creep than to the plastic state.
Metals such as mild steels have a plastic phase that occurs after the elastic phase. This phase is non-linear and irreversible.