What's the difference between rubber and plastic?

Rubber materials (aka elastomers) generally have greater elastic elongation range than plastics. For example natural latex rubber can have an elongation of 700%.

Rubber materials are usually cross-linked molecular chains while the (meltable) thermoplastics are not cross linked. However, thermoset plastics which do not melt are cross linked like rubber.

Rubber materials have a poisson ratio of 0.5 while plastics have a lower value.