The policy category of 'strategic science' is enjoying increasing popularity. Through a case study of membrane technology, as a scientific-technological field and as a newly-emerging 'world' of membranes, this paper shows how such policy labels and rhetorical claims are filled up, and new social realities are created. The key step is the way in which promises put forward, and expectations being voiced, require actors to position themselves with respect to a future technology. Thus a shared agenda is built up at the same time as a 'world of membranes gels'. The rhetorical space opened up by strategic science and technology policy is then filled up by actual strategic sciences and technologies.