  Although there are theoretical predictions [\textit{Eur.~Phys.~J.~E}
\textbf{41} (2018) 110] for the rich phase behaviour of colloidal cubes mixed
with non-adsorbing polymers, a thorough verification of this phase behaviour is
still underway; experimental studies on mixtures of cubes and non-adsorbing
polymers in bulk are scarce. In this paper, mixtures of hollow silica nanocubes
and linear polystyrene in \textit{N,-N-}dimethylformamide are used to measure
the structure factor of the colloidal cubes as a function of non-adsorbing
polymer concentration. Together with visual observations these structure
factors enabled us to assess the depletion-mediated phase stability of
cube-polymer mixtures. The theoretical and experimental phase boundaries for
cube-depletant mixtures are in remarkable agreement, despite the
simplifications underlying the theory employed.
