Real-time X-ray microtomography is used to study the underlying mechanisms of the yielding and collapse of a closed-cell metallic glass foam (see figure). Intercellular and intracellular deformations upon compressive loading are examined in situ. A shear-stability analysis reveals that glassy foams obey the same universal yield criterion as zero-temperature glasses, suggesting a link between the floppy modes in a glass and the buckling instabilities in a stochastic cellular structure.