塑料是以单体为原料，通过加聚或缩聚反应聚合而成的高分子化合物(macromolecules)，可以自由改变成分及形体样式，由合成树脂及填料、增塑剂、稳定剂、润滑剂、色料等添加剂组成。
Plastics are macromolecules which are synthesized from monomers by addition or condensation. They can freely change their composition and shape. They are composed of synthetic resins and additives such as fillers, plasticizers, stabilizers, lubricants and colorants.
塑料的主要成分是树脂。树脂是指尚未和各种添加剂混合的高分子化合物。树脂这一名词最初是由动植物分泌出的脂质而得名，如松香、虫胶等。树脂约占塑料总重量的40%～100%。塑料的基本性能主要决定于树脂的本性，但添加剂也起着重要作用。有些塑料基本上是由合成树脂所组成，不含或少含添加剂，如有机玻璃、聚苯乙烯等。
The main component of plastics is resin. Resin is a kind of macromolecule compound which has not been mixed with various additives. The term resin was originally named for lipids secreted by animals and plants, such as rosin, shellac, etc. Resin accounts for 40%-100% of the total weight of plastics. The basic properties of plastics mainly depend on the nature of resins, but additives also play an important role. Some plastics are basically composed of synthetic resins without or without additives, such as plexiglass, polystyrene, etc.