A bubble raft is an array of soap bubbles that models the structure and dynamics of a real crystal consisting of atoms or ions. Most bubble rafts consist of a single layer and are therefore 2-dimensional; even so, they exhibit many of the same kinds of phenomena as seen in 3-dimensional crystals. The bubbles in a bubble raft are typically about 1 mm in diameter. If all the same size, the bubbles will self-assemble into a hexagonal array, the same as the arrangement of atoms in the {111} planes of a face centered cubic metal such as copper of aluminum.