Abstract: Smooth-surfaced, free-flowing, rigid, spherical, hollow microcapsules having non-porous shell walls consisting of essentially homogeneous, non-vitreous metal oxide in predominantly polycrystalline state, which have at least one shell having over the entire outer surface thereof one or more coatings of material of the class consisting of ceramic oxide, metal or pyrocarbon, which contain for storage and transport within said shell or shells preselected gases, solids or liquids suitable for use in fusion targets are described together with methods for their production.