Plastics have become the most important material in many fields and applications. They are lightweight, some have excellent optical properties, some are electric and thermal insulators, and in general they are easier and less expensive to make and to process into a final product. Some of their properties exceed the properties of more traditional materials, while in other areas they are no match to conventional engineering materials. Polymers are differentiated in three categories: thermoplastics, thermosets, or elastomers. Thermoplastics in turn include a special family, called thermoplastic elastomers. However, all these material have in common that they are made of large molecules See More..