Tilda Swinton is hard to classify as a performer because flux and mutability have become her signature qualities. One enduring element in her repertoire, however, can be brought into focus through Lauren Berlant's concept of "flat affect." Typically described as mysterious, otherworldly, or ethereal, Swinton often brings to her screen and live performances a quality or atmosphere that contradicts the conventional expectations of feminine emotional expressiveness and legibility in popular cinema. As a contribution to this special issue on Berlant's work, my article traces Swinton's styles of flat affect as an aesthetic relationality across a number of films, including Teknolust, Michael Clayton, The Deep End, and Orlando. My reading of Swinton's capacity for flatness places it within the history of her unusual facility to cross between independent and more popular cultural forms and to set femininity as genre in motion as she does so. Famous for embodying gender ambiguity since her performance as Orlando, Swinton's association with androgyny as a pre-queer promise of limitlessness folds femininity back upon its historical conventions and imperatives. In tracing the history of Swinton's gender fluctuations, this article concludes by reflecting on some of the failures of feminist and queer language to articulate the nuances of affective registers; androgyne, butch, tomboy, trans, and genderqueer designate styles of gendered and sexual embodiment, but these do not extend satisfactorily to aesthetic moods and atmospheres. Closing with a discussion of "offgender" flux, the article considers Swinton's recent twinning with David Bowie to open up how her performances reinvent affective genres while calling forth their histories and temporalities.Keywords Tilda Swinton . Lauren Berlant . Flat affect . Gender and genre . Feminist and queer theory When Lauren Berlant writes about contemporary genres of intimate sociality, she extends a concept of structural repetition from film theory into a more generalised understanding of subjectivity as inextricable from the popular modes of its formation. For Berlant, the cinema has always been integral to the ways in which modern culture has produced affective subjects who inhabit its social and political spaces through fantasy landscapes, the mise-en-scène of which structure our everyday lives as much as they do the fictions we consume. Reading these shifting genres as historical and Int J Polit Cult Soc (2015) 28:243-271