PurposeSocial and environmental reports have become an increasingly regulated area of corporate reporting and communication. Nevertheless, the substance and level of detail present in such disclosures is largely at the discretion of companies, which has implications for the value of such disclosures to stakeholders. The purpose of this study is to shed light on social visibility as a determinant of the variation in substance found in social disclosures in order to understand underlying reasons for why some firms offer more substance than others in their social disclosures.Design/methodology/approachBased on a number of hypotheses, which are combined into social visibility, the paper investigates whether a firm's social visibility is a determinant of substance in social disclosures. To this end, the case of modern slavery statements is used as a recently introduced and legally mandated form of social sustainability disclosures.FindingsThe findings suggest that social visibility can explain part of the variation in the substance of social disclosures. However, for the remaining part, it is argued that substance in social disclosures can also be driven by institutional logics, which shape organizational outcomes in specific contexts, but are largely unobservable.Originality/valueThis article contributes new insights to the literature on the relationship between corporate social visibility and the substance of social disclosures.