Final answer:
Outer packs are designed to be stacked using a hexagonal closest packing arrangement, which is more efficient in terms of coverage of the area.
Step-by-step explanation:
The stacking of outer packs is designed using a hexagonal closest packing arrangement. Hexagonal closest packing consists of two alternating layers (ABABAB...), where atoms are packed as compactly as possible. This arrangement provides a more efficient packing arrangement in terms of coverage of the area. Hexagonal packing yields 91 percent coverage compared to square packing, which covers only 78 percent of the area.