The Third Law of Thermodynamics states that as the temperature of a pure substance moves toward absolute zero (the mathematically lowest temperature possible) its entropy, or the disorderly behavior of its molecules, also approaches zero. The molecules should line up in an orderly fashion.
Ice seems to be the exception to that rule. While the oxygen atoms in ice freeze into an ordered crystalline structure, its hydrogen atoms do not.
Researchers at the University of Maryland are using meta-materials, which mimic the behavior of ice but are created out of completely different substances, to try and figure out why water ice doesn't completely conform to the Third Law of Thermodynamics.