Porous polymers are a class of porous media materials in which monomers form 2D and 3D polymers containing angstrom- to nanometer-scale pores formed by the arrangement of the monomers. They may be either crystalline or amorphous. Subclasses include covalent organic frameworks (COFs),  hydrogen-bonded organic frameworks (HOFs), metal-organic frameworks (MOFs), and porous organic polymers (POPs). The subfield of chemistry specializing in porous polymers is called reticular chemistry.