Size Exclusion Chromatography (SEC) is the dominant mode of separation for polymers. It is based on the discrimination of individual sample components by the pores of the packing material. Large sample molecules cannot or can only partially penetrate the pores, whereas smaller molecules can access most or all pores. Thus, large molecules elute first, smaller molecules elute later, while molecules that can access all the pores elute last from the column.

SEC is usually called Gel Filtration Chromatography when working with water-soluble polymers, or Gel Permeation Chromatography when working with organic-soluble polymers.