Plastic can be generally defined as a macromolecular substance formed from linking up of monomers through the use of covalent bonds. Using two or more monomers in the linking process leads to the formation of the copolymer. Thermoplastics and thermosets make up the wider classification of plastics. Thermoplastics are those that exist as single discrete long-chained molecules as opposed to thermosets which exist as cross-linked network structures. The manufacture of plastic products using different processing techniques and materials makes their identification through visual inspection practically impossible.