Ice is commonly thought to have a hexagonal crystal structure, as reflected in the symmetry of snowflakes. Along with cubic ice, which is found in the upper atmosphere, these are the only crystalline forms of ice found in nature so far. Now, Takahiro Matsui and colleagues at Okayama University in Japan suggest that this is merely the tip of the iceberg. Using classical molecular dynamics simulations, the team found over 300 new kinds of porous ice structures derived from zeolite frameworks and space fullerenes. Despite being a vast increase over the 17 ice polymorphs found experimentally so far, they only exist at very low – even negative – pressures and temperatures near absolute zero.