The behaviour of a compressed flange with respect to local buckling depends on the geometry of the flange and the properties of the material (SS1312 and Weldox 700 steels) of which the flange is made. The method by which these variables are taken into account in the codes is based on the definition of a so called slenderness. This measure is then taken as the only variable governing the instability characteristics. Although this is a well established procedure not only for flange buckling but virtually any instability problem of any structural element, one may suspect that it is an over-simplification. This paper examines the accuracy of the above mentioned approach with respect to large variations in the yield strength.