Today's commonly used proppants include various sands

Since the earliest fracturing treatments more than 50 years ago, many different materials have been used including sand, glass beads, walnut hulls, and metal shot. Today's commonly used proppants include various sands,resin coated frac sand,resin coated silica sand, intermediate-strength ceramic proppants, and sintered bauxite proppant—each employed for its ability to cost-effectively withstand the respective reservoir closure stress environment. As the relative strength of the various materials increases, so too have the respective particle densities, ranging from 2.65 g/cm3 for sands to 3.4 g/cm3 for the sintered bauxite.  Unfortunately, increasing particle density leads directly to increasing degree of difficulty with proppant transport and a reduced propped-fracture volume for equal amounts of the respective proppant, thereby reducing fracture conductivity. Intuitively, one expects that a lesser-density proppant would be easier to transport, allowing for reduced demands on the fracturing fluids, and if it had sufficient strength, would provide increased width, and hence, enhanced fracture conductivity