Simply stated, the " high-molecular substances" as referred to by the Japan Industrial Standard mean " substances with very high-molecular weights synthesized chemically." Substances are classified into low-molecular, intermediate-molecular, and high-molecular substances according to their molecular weights. For example, the molecular weight of oxygen is 32 and that of sugar is 342.

On the other hand, the molecular weights of rubber and proteins exceed 10000. Natural "high-moleculara?? compounds include, natural resins such as natural rubber and rosin, cellulose, silk, proteins, and many other substances. The substances produced in imitation of these substances are synthetic rubber, synthetic resins, and synthetic fiber. Thus, plastics are high-molecular compounds produced artificially. They are called " synthetic resin" or simply " resin" in comparison to natural resin.

The definition of plastics

The Japan Industrial Standard (JIS K 9600-1977) defines "plastics" as "solids artificially formed into useful shapes using high-molecular substances as main raw materials. However, fiber, rubber, paints, and adhesives are excluded."