What is closest packing?

Closest packing refers to an arrangement of spheres in three-dimensional space that maximizes the density of the packing. The most efficient arrangements are face-centered cubic (FCC) and hexagonal close packing (HCP), both of which achieve a packing efficiency of about 74%. In these configurations, each sphere is surrounded by 12 others, optimizing the use of available space. Closest packing is significant in materials science, particularly in the study of crystalline structures.