The experience of theatre audiences participating in contemporary “immersive” productions is often regarded as an enhanced and more effective iteration of the illusionistic apparatus of bourgeois theatre, wherein the materiality of the medium is rendered “transparent” to its users through digital technologies. I argue that this interpretation is rooted in an epistemological misunderstanding, which I term the regressive assimilation of media. This phenomenon occurs when the epistemic power of a newer medium, combined with the ease and frequency of its use, reconfigures the understanding and experience of an older medium through a feedback mechanism, effectively assimilating its cognitive and aesthetic functions. In this case, the screen assimilates the architectural space of the theatre, including the box-set stage and audience hall. I propose a distinction between the notions of immersive experience and immersive theatre. Immersive experience, exemplified by environments such as anechoic chambers or sensory deprivation tanks, heightens an individual’s proprioceptive awareness. In contrast, immersive theatre arises from a highly constructed and relational context involving the participants or “immergents”. Finally, I argue that theatre is inherently immersive—independent of its engagement with digital technology—precisely because of its mediated and reflexive nature.