This paper engages with the debate on niche-regime interactions in sustainability transitions, using a study of plant-based milk and its struggles against the entrenched liquid dairy-milk regime, which has various sustainability problems. Plant-based milk is under-studied, so our empirical contribution consists of an exploration of its diffusion in the UK. We make three conceptual contributions. The first calls for a bidirectional analysis that addresses niche-oriented activities by incumbent actors, in addition to the outward-oriented activities by niche advocates presented in most studies of niche-regime interaction. The second contribution nuances Smith and Raven’s fit-and-conform and stretch-and-transform typology: using a societal embedding framework which distinguishes four environments, we suggest that hybrid patterns are possible in which innovations follow a ‘fit’ pattern in one environment but ‘stretch’ in another. The third contribution highlights the potential role of cultural meanings in galvanizing transitions by eroding positive associations that support the regime and stabilise consumer purchasing.