Generally, polymers can be classified according to their thermal and mechanical properties
into thermoplastics, thermosets and elastomers. Thermoplastics are amorphous or semicrystalline
polymers that soft or melt during heating and solidify during cooling. The
heating/cooling/heating process can be repeated without perceptible changes in thermal and
mechanical properties of thermoplastics. Thermosets during heating undergo chemical
changes and this process is irreversible. Elastomers can be vulcanized (cross-linked under
assistance of heat, light, or special chemicals like sulfur, peroxides) that makes them
reversibly stretchable for small deformations but vulcanization is the irreversible process.