Nigerian manufacturing firms have embraced environmental, social and governance (ESG) reporting with enthusiasm, driven by the dual pressure of accessing sustainable finance and maintaining legitimacy with international investors and regulators. Yet the relationship between what firms disclose and what happens inside the factory remains largely unexamined. This article develops an industrial-sociological account of ESG greenwashing as a form of organisational decoupling. Drawing on neo-institutional theory, it argues that ESG reporting in Nigerian manufacturing is best understood not as a transparency failure but as a legitimacy strategy: firms adopt the formal structures and vocabularies of sustainability to satisfy external audiences while buffering internal production practices from the implications of those commitments. The study employs a sequential mixed-methods design: content analysis of sustainability reports from thirty listed manufacturing firms (2022–2025) using the Global Reporting Initiative (GRI) index, followed by industrial ethnography and semi-structured interviews with forty factory workers and ten health, safety and environment (HSE) managers in Lagos and Port Harcourt industrial estates. Findings reveal systematic policy–practice decoupling: disclosed commitments to fair wages, safe conditions, and pollution control are contradicted by shop-floor accounts of wage arrears, safety shortcuts, and unreported emissions. Decoupling is sustained by weak external verification, investor preference for disclosure over enforcement, and an organisational field in which the reputational cost of greenwashing remains lower than the cost of genuine compliance. The article contributes a decoupling based account of ESG greenwashing that identifies the mechanisms sustaining it, and argues that sustainable finance governance must shift from disclosure-centric to verification-centric accountability. Keywords: ESG, greenwashing, decoupling, neo-institutional theory, industrial sociology, Nigerian manufacturing