Abstract: Microsphere wet cake is mixed with a processing aid effective to prevent agglomeration and surface bonding of the microspheres, and thereafter removing water by drying with continuous mixing, optionally also under reduced pressure, i.e. vacuum drying. By the control of the application of heat and balancing temperature and the mixing, and optionally also the reduced pressure, it is possible to also control expansion of the microspheres from substantially none to substantially theoretical limits of expansion.The processing aid 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, dry inorganic pigments or filler materials, and the like, and related organic materials.