Microsphere beads are mixed with a surface barrier solid, liquid or mixture of such a liquid with a solid effective to prevent agglomeration and surface bonding of the microspheres; by the control of the application of heat and balancing temperature and active mixing, removal of water from and expansion of the microsphere is achieved. Microsphere densities of as low as 0.005 to less than 0.015 g/cm.sup.3 are realized. The surface barrier solid, liquid or mixture of such a liquid with a solid in the present invention is any one of a wide diversity of materials which meet the requirements of the intended function, i.e., to prevent the agglomeration of the microspheres during the process. Suitable materials include, by way of example, fillers, pigments, plasticizers, diluents, extenders, monomers and oligomers and the like.