Plastics can be divided into four groups according to their physical properties:

Thermoplastics are plastics which can be soft, viscoplastic or hard. They are melted by heating and are then malleable. This is due to their internal composition of unbranched or branched chain molecules which are uncrosslinked. The far bigger part of the nowadays industrially manufactured Polymers (approx. 80 % of the total production) belongs to this group.

Elastomere are slightly cross-linked, are often of comparatively long chains and have elastic properties at ambient temperature. Depending on the relation between application temperature and glass transition temperature they are hard upto hard-elastic or soft-flexible. It is one of their basic characteristics that they decompose before they melt. Elastomers distinguish themselves from the thermoplastics by the cross-linking of macromolecules. In contrast to thermosets elastomers contain comparatively long, uncrosslinked and entangled molecular moieties

Thermoplastic Elastomers
Thermoplastic Elastomers combine the mechanical properties of vulcanized elastomers (rubber) at ambient temperature and the processability of thermoplastics.

Duromers harden when heated up and do not become soft again. The hardening is achieved by spatially focused, mostly covalente cross-linking of Polymer molecules. Duromers are currently quantitatively less important than thermoplastics.