The present paper is dedicated to the experimental characterization of hollow section shapes’rotational capacity. The purpose of the research works dealt with herein is to establish a direct dependence of the rotation capacity Rcap to a newly defined cross-sectional overall slenderness λCS. In other words, the intention is here to investigate how ductility can be associated with cross-section slenderness, in the perspective of providing designers with guidance on when allowed/not allowed to resort to plastic analysis and design. The paper describes a series of bending tests that aimed at characterizing experimentally the relationship between ductility (Rcap) and cross-section compactness (λCS). Besides, numerical F.E. models created in the purpose of being substituted to physical tests are described, and tested against the experimental results. The F.E. models were shown capable of nicely replicating the experimental behavior of H.S.S. beams. Therefore, they can safely be substituted to physical tests and be subsequently used in extensive numerical studies, which are currently under development.