This type of crystal structure has a cubic unit cell with atoms centered at all eight corners, plus an atom centered in the middle of each of the six cube faces. The atoms touch each other along the face diagonal, and along the plane bisecting the cube in each of the three directions possible. So therefore each atom would be touching twelve other atoms. This pattern holds four atoms per unit cell. The atomic packing factor for a Body Centered Cubic crystalline structure is 0.74, which is the highest possible value for any arrangement of spheres of identical radius. The other arrangement that has this close packed arrangement is the Hexagonal Close Packed.
Some of the materials that are composed of Face Centered Cubic unit cells at room temperature include Copper, Nickel, Aluminum, Lead, Silver, Platinum, and Gold. Note that these metals tend to have high density. This is directly a result of the high atomic packing factor. They also tend to be quite ductile materials. This is due to their structure having four different so called "slip planes," planar vectors along which the layers of atoms are more likely to slide apart.