Bénard cells are convection cell structures that spontaneously form in viscous mediums, such as water, when it is heated from bellow while cooled from above, in such a case the heated water tries to rise while the cool water decends. The system then self-organize into a set of hexagonal cells with cool water flowing down on one side and heated water rising on the other. Bénard cells are of interest within complexity theory because they illustrate well the process of self-organization.