Colloids are a type of mixture that is in between a homogeneous solution and a heterogeneous suspension. They have particle sizes that are big enough to be visible, but the particles do not settle out over time. Colloids exhibit the Tyndall effect, and they scatter light. Also, colloids can't be separated by filtration. All colloids have a dispersed substance in a dispersion medium. Some common colloids are fog, smoke, foam, gels, and emulsion. The dispersed substance and dispersion medium can be solid, liquid, or gas. An emulsion is two immiscible liquids that are dispersed through one another. Colloids are like a homogeneous solution in some ways, but like a heterogenous suspension in other way.