Paper occupies a special place in histories of knowledge. It is the substrate of communication, the stuff of archives, the bearer of marks that make worlds. For the early-modern period in particular we now have a wealth of studies of ‘paper tools’, of the ways in which archives were assembled and put to use, of the making of lists and transcribing of observations, and so on. In other fields, too, attention has turned to the materiality of information. How far is it possible to draw a stable methodology out of the insights of literary and book historians, bibliographers, anthropologists, and those working in media studies? Do these diverse fields in fact refer to the same thing when they talk of paper, its qualities, affordances and limitations? In attempting to answer these questions, the present essay begins in the rich territory of early-modern natural philosophy – but from there opens out to take in recent works in a range of disciplines. Attending to the specific qualities of paper is only possible, I argue, if it is understood that paper can be both transparent and opaque depending on the social world it inhabits and helps to constitute. Paper flickers into and out of view, and it is precisely this quality that constitutes its sociomateriality.