High Quality Content by WIKIPEDIA articles! Ice XI is the proton-ordered form of Ih, the most common form of ice. Different types of ice, from ice II to ice XV, have been created in the laboratory at different temperatures and pressures. The total internal energy of ice XI is about one sixth lower than ice Ih, so in principle it should naturally form when ice Ih is cooled to below 72K. The low temperature required to achieve this transition is correlated with the relatively low energy difference between the two structures. Water molecules in ice Ih are surrounded by four semi-randomly directed hydrogen bonds. Such arrangements should change to the more ordered arrangement of hydrogen bonds found in ice XI at low temperatures, so long as localized proton hopping is sufficiently enabled; a process that becomes easier with increasing pressure. Correspondingly, ice XI is believed to have a triple point with hexagonal ice and gaseous water at (~72 K, ~0 Pa).