Field-flow fractionation (FFF) is a family of techniques used to characterize macromolecules, colloids, and particulate materials, primarily by size, but in some cases by composition as well. FFF has many similarities to chromatography, but it also has several unique differences. Like liquid chromatography, small amounts of material are separated as they are carried through a channel by a stream of liquid. Certain materials move more slowly through the channel than others, and the amount of carrier liquid required to sweep a given material from inlet to outlet is used to characterize particular features of the material.