A filler component for making an investment casting slurry, which comprises: a major portion of finely divided silica, aluminum silicate, alumina, zircon, or mixtures thereof; and a minor portion of one or more finely divided materials having particles in which, on average, at least one dimension of the particle is at least about four times greater than at least one other dimension of the particle. Typically, the particles are of generally plate-like or needle-like shape.