The use of social media in the public sector changes the professionals' everyday work practice. This paper sheds light on the emerging challenges of using social media as a part of work, based on the analysis of three contexts within the public sector in Sweden and through the lens of sociomateriality and affordances. The approach is interpretive field studies with a narrative analysis, where we interpret and analyse key elements of the storylines, focusing on the transition to social media use among professionals (nurses, municipal communicators, and physicians) in the three contexts. Social media enables an open work environment where information is visible and potentially spreadable to an unknown audience. The process of interacting with an unknown audience and finding a professional tone is analysed here as context collapse. The unknown, and at times imagined complex audience, makes it hard to balance the seesaw between friendliness on the one hand and an authoritative tone on the other; a tonality which leaves most of the potential audience unreached. The interplay between social media and the professionals shapes the professionals’ practice. We analyse this interplaying practice more specifically, as sociomateriality in action.