There four main types of colloids are sols, emulsions, foams and aerosols. All of these mixtures share the major properties of colloids. That is, they are solutions containing particles between 1 and 1000 nanometers in size that are dispersed throughout the solvent, but are not chemically bound to molecules of the solvent.
Colloids are classified based on the phases their components are in. Solids, liquids and gases may all be present in colloidal suspensions. Sol is the term used to refer to colloids which consist of solid particles suspended in a liquid solvent. An example of a sol colloids is proteins suspended in the fluid matrix of milk. Emulsions are colloidal mixtures which consist of "beads" of one liquid suspended in another liquid. An example is a salad dressing, which consists of droplets of oil suspended in water. Certain substances, including egg, encourage emulsification when added to mixtures. Foams are a type of colloid formed when gas particles are suspended within a liquid or gas. An example is shaving cream. Aerosols are yet another type of colloid, which consists of small particles of liquid dispersed throughout a gas medium. Hair spray, body spray or any other substance in an aerosol can falls into this category.