Biomolecular condensates selectively compartmentalise and organise biomolecules within the crowded cellular milieu, and are instrumental in some disease mechanisms, including aiding RNA virus replication. Upon infection, many RNA viruses form biomolecular condensates that are often referred to as viral factories. The assembly mechanism of these viral factories remains poorly defined, but involves transient, non-stoichiometric protein/RNA interactions, posing challenges for their characterisation. Here we present HDX-MS data of NSP2 and NSP5, in a biomolecular condensate to study the mechanism of condensate assembly.