The particle size distribution of a first fly ash is compared to an ideal particle size distribution that was empirically developed to provide a resin melt with a lower viscosity as more fly ash is added. A second fly ash material is similarly compared to the ideal curve and then is blended or optimized to provide an optimum filler for use with a suitable resin or similar material. Additional fly ash materials may be similarly compared and blended. Additional additives may be added for, among other things, foaming and coloration.