The bulk density for porous materials is defined as the density measured
by considering the overall volume of the material; including pore
volume. The tap or pack density is obtained from filling a container with
sample material and vibrating it to obtain near optimum packing. Such a
measurement is of great interest in packing and shipping items like
bulky products. Tap density is not an inherent property of a material
but depends on particle size distribution and shape as well as measurement
techniques.