The
surfaces of each box must be parallel to one of the three planes: xy,
xz and yz in Fig. 5. The boxes should also be arranged such that s is
no longer in height than the container and the volume of the envelope
cuboid (see Fig. 5(a)) of s is minimized. Let ls and ws be the
length and width (Generally the length is not shorter than the
width) of the envelope cuboid. The filling rate of s is defined as: