Wood flour is finely pulverized wood that has a consistency fairly equal to sand or sawdust, but can vary considerably, with particles ranging in dimensions from a fine powder to roughly that of a grain of rice.  Most wood flour manufacturers are able to create batches of wood flour that have the same consistency throughout.  All high quality wood flour is made from hardwoods because of its durability and strength.  Very low grade wood flour is occasionally made from sapless softwoods such as pine or fir.