The shape and size distribution of polystyrene (PS) compartments formed during emulsion electrospinning in a poly(vinyl alcohol) fiber is investigated. Stimulated emission depletion microscopy is employed to image the compartments with subdiffraction (super) resolution. The size distribution of the emulsion droplets in the spinning solution emulsions is found to be the key factor for fiber and compartment morphology. By varying the emulsification method, it is demonstrated that fibers spun from miniemulsions are characterized by a homogeneous distribution of PS compartments with no indication for coalescence or breakup of PS droplets. Coarse emulsions are prone to develop fiber instabilities associated with large PS domains. The domains are irregularly distributed in the fiber. Above a critical size of domains, breakup of these domains in two daughter domains is observed. The size dependence of the emulsion droplet breakup is explained by fluid dynamics.