The polymer, which can be stretched and retains its original status...

Synthetic rubber is any vulcanisable rubber like polymer, which is capable of getting stretched to twice its length. However, it returns to its original shape and size as soon as the external stretching force is released. Thus, synthetic rubbers are either homopolymers of $1, 3$ - butadiene derivatives or copolymers of $1, 3$ - butadiene or its derivatives with another unsaturated monomer.

Buna-N is an example of synthetic rubber.