I. Resins. Resins are amorphous organic solids or sticky organic liquids or semi-solids which usually have a typical metallic lustre and are often transparent or translucent Natural resins are secreted or flow out of plants (and some insects) when they are cut or
wounded. They can harden when exposed to the air to form brittle, non-crystalline solids. Resins are insoluble in water but soluble in ether, ethanol and other organic solvents. Examples of natural resins are amber (fossil resin) and shellac.
II. Plastics. A plastic is a substance which is capable of being moulded whereas a resin lacks this property. Typical plastics on heating become soft but do not give mobile melts. In contrast, resins on heating give mobile melts. Plastics usually have much higher molecular mass than resins. Nevertheless, this differentiation is not very clear and the two terms are often used interchangeably .