We demonstrated a practical microfluidic approach to fabricate extremely monodisperse millimeter-sized poly(divinylbenzene) (PDVB) foam shells with the comparable double emulsion templates. At millimeter scale, the emulsification process was more complex and more difficult to control due to the very large characteristic sizes and velocities. A new kind of three-dimension co-axial microfluidic chip including a Y-shaped compound channels was designed to maintain more stable and robust flow field and regular emulsification. The hydrodynamic features of the double-emulsion droplet formation were investigated. The results showed perfect encapsulation and continuous emulsification could be obtained by one-step dripping (Ca-outer (0.018,0.09)). The size of the outlet channel would be comparable with the target droplet. Besides, droplet diameters could similarly be plotted as a function of capillary number close to the general microfluidic ones. After photo-polymerization and supercritical drying, spherical and concentric PDVB foam shells were obtained to satisfy the inertial fusion energy experiments with large diameter (3-5.45 mm), thin wall thickness (50-250 m), low density (50-300 mg/cm(3)), and a less than 0.1% polydispersity. POLYM. ENG. SCI., 58:1184-1192, 2018. (c) 2017 Society of Plastics Engineers