Plastic is derived from organic substances including crude oil, salt, cellulose, coal and natural gas. Crude oil, one of the main ingredients of plastic, is a complex compound that must be broken down into fractions (mixtures of compounds made up of carbon and hydrogen) in order to be used effectively.
There are two major processes used to make plastic: polymerisation and polycondensation. Although there are several different types of plastics, the two main families are thermoplastics and thermosets. Thermoplastics soften when they are heated and then become hard again once they cool. Thermosets cannot be softened once they have been moulded.