This paper introduces a materialist approach to Isin’s concept of ‘acts of citizenship’ to call for an attention to the lively and agential materials that mediate citizenship claims. It describes two ways in which materialism helps progress conceptualisations of citizenship. Firstly, it demonstrates the ways in which a materialist viewpoint forces a reconsideration of ‘acts of citizenship’ as undertaken by heterogeneous collectives, rather than them being the sole responsibility of human actors. Secondly, it suggests that, because acts of citizenship arise out of socio-material entanglements, they may exceed the apparent intentions of human subjects. This paper argues that materials are more than bystanders in claims to citizenship; they actively mediate and facilitate encounters through which political claims are made. This argument is developed through a detailed empirical study of the materials permitted to circulate from Immigration Removal Centres during a community exchange project organised by the charity Music in Detention.