An experimental and numerical analysis is performed to investigate the effect of attaching poor conducting ribs on a vertical heated flat prate. Accordingly, a test cell is constructed and a mathematical model is developed. The ribs are made of a poor conducting material (plexiglass). The present work is intended to study the suppression of free convection from a vertical plate with ribs attached on the surface. The effects of rib height to span ratio and Rayleigh number are investigated experimentally and numerically for air as the working fluid. It has been found that adding ribs an the surface can reduce the rate of free convection heat transfer by as much as 75% compared with a bare plate. Rather complex recirculatory flow patterns are predicted in the space between the ribs at high Rayleigh numbers.