The objective of this paper is to analyse the effect of professional, technical and relational background (human and social capital) of outside directors on promoting firm CSR disclosure. Following the Hillman et al. (2000) taxonomy of board members, we classify outside directors as business experts, support specialists and community influentials, and examine whether business and technical expertise or political ties in the boardroom affect CSR disclosure.This study confirms that not all outside directors are equally effective in improving CSR disclosure and that only certain kinds of outside directors, those classified as support specialists, help increase it. On the other hand, our findings also show that directors with previous experience as politicians affect CSR disclosure negatively, probably due to their interests in safeguarding their reputation within the company against public scrutiny and in protecting their political connections. In addition, our set of analysis with interaction effects reveals that powerful CEOs have the incentive to promote CSRrelated strategies and to press business expert and support specialist directors to enhance profitable sustainability strategies and transparency in its disclosure. Nevertheless, powerful CEO effect is not enough to compensate the negative role of political directors on CSR reporting. Therefore, this paper supports the theories that appeal for analysing the multiple configurations of corporate governance mechanisms by adopting a "holistic approach" and the need to combine them in order to analyse their impact on CSR behaviour.