During TTIP negotiations, the European Commission was severely criticized by civil society organizations and public opinion for its secrecy regarding negotiation strategies and priorities. The Commission responded by making some negotiating texts publicly available. This article explores the implications of increasing transparency in trade negotiations. Drawing on negotiation, politicization, and informal governance literature, it examines how the Commission’s choice for a partial transparency approach had three paradoxical effects on negotiations. First, greater transparency did not help the public perception of TTIP. Second, greater transparency increased the EU’s bargaining leverage but led to a low degree of negotiating discretion for the Commission. Finally, greater transparency transformed the nature of the negotiating process by making it more informal, allowing bargaining parties to act outside the public scrutiny. This contribution solves these transparency puzzles by showing that partial transparency is a double-edged sword. Whilst greater transparency has become an important legitimation strategy in EU trade governance, adopting a partial transparency approach fuelled public protest instead of muting it and led to the failure of the negotiations.