What IS an Elastomer

Any low-crystallinity or amorphous, high molecular weight polymer with sufficiently flexible chains can in principle be made into an elastomer by crosslinking the chains. Such a polymer gel is an elastomer at 20+ kelvins above its glass temperature Tg.
Crosslinks can be chemical (thermoset elastomers) or physical (TPEs)

Any low-crystallinity or amorphous, high molecular weight polymer with sufficiently flexible chains can in principle be made into an elastomer by crosslinking the chains. Such a polymer gel is an elastomer at 20+ kelvins above its glass temperature Tg.