Flange edge stiffeners can increase the ultimate moment capacity of cold-formed channel sections up to their post-yielding (inelastic) capacity. This paper investigates the post-yielding behaviour under bending of cold-formed channel sections with partially stiffened elements. The relevant literature was reviewed, experimental studies were carried out and a semi-empirical analysis was performed. Experimental and numerical analysis was undertaken of 40 cold-formed channel sections, each with a partially stiffened element. The results were compared with the existing Australian design rules and revisions are proposed to these rules. In addition, by using the test observations and the yield line mechanism model, the ultimate capacity of the tested sections was determined and compared with the test results. The model was found to provide accurate and reliable capacity predictions for slender cold-formed channel sections under bending.