It is unclear how the materials properties of biomolecular condensates are determined by the interactions between their components, and thus how materials properties change as a function of composition. The Rosen lab previously identified seven proteins that can be used to reconstitute S. cerevisiae P-bodies in vitro. Biochemical experiments revealed that these components assemble and phase separate through combinations of homotypic interactions and heterotypic interactions between the different P-body components in physiological conditions. This in vitro reconstruction provides a platform to understand the materials properties of a multicomponent biological condensate and how they arise from these different types of interactions. Biological condensates are complex mixtures that contain both viscous and elastic properties. To measure the viscoelastic properties of reconstituted P-bodies, I am using microrheology and atomic force microscopy (AFM) techniques. Characterizing the materials properties of a condensate may help us understand its composition, biological functions and mechanism of formation.