The presence of these many allotropes makes machining plutonium very difficult, as it changes state very readily. For example, the α phase exists at room temperature in unalloyed plutonium. It has machining characteristics similar to cast iron but changes to the β phase (beta phase) at slightly higher temperatures. The reasons for the complicated phase diagram are not entirely understood; recent research has focused on constructing accurate computer models of the phase transitions. The α phase has a low-symmetry monoclinic structure, hence its poor conductivity, brittleness, strength and compressibility.